OTHER SPECULATIONS.

The nebular hypothesis of Laplace required a rotating mass of fluid which at successive epochs became unstable from excess of motion, and left behind rings, or more probably, perhaps, lumps, of matter from the equatorial regions. To some thinkers was suggested a different view of things, according to which it was not necessary to suppose that one part of the system gravitationally supported another. The whole might consist of a congeries of discrete bodies, even if these bodies were the ultimate molecules of matter. The planets might have been formed by the gradual accretion of such discrete bodies. On the view that the material of the condensing solar system consisted of separate particles or masses, we had no longer the fluid pressure which was an essential part of Laplace's theory. Faye, in his theory of evolution from meteorites, had to throw over his fundamental idea of the nebular hypothesis, and formulated instead a different succession of events of which the outer planets were formed last, a theory which had difficulties of its own. Professor George Darwin had recently shown, from an investigation of the mechanical conditions of a swarm of meteorites, that on certain assumptions a meteoric swarm might behave as a coarse gas, and in this way bring back the fluid pressure exercised by one part of the system on the other, which was required by Laplace's theory. One chief assumption consisted in supposing that such inelastic bodies as meteoric stones might attain the effective elasticity of a high order which was necessary to the theory through the sudden volatilization of a part of their mass at an encounter, by which what was virtually a violent explosive was introduced between the two colliding stones. Professor Darwin was careful to point out that it must necessarily be obscure as to how a small mass of solid matter could take up a very large amount of energy in a small fraction of a second.

HELMHOLTZ'S DISCOVERY.

The old view of the original matter of the nebulae, that it consisted of a "fiery mist,"

"a tumultuous cloud, Instinct with fire and niter,"

fell at once with the rise of the science of thermodynamics. In 1854, Helmholtz showed that the supposition of an original fiery condition of the nebulous stuff was unnecessary, since in the mutual gravitation of widely separated matter we had a store of potential energy sufficient to generate the high temperature of the sun and stars. We could scarcely go wrong in attributing the light of the nebulae to the conversion of the gravitational energy of shrinkage into molecular motion. The inquisitiveness of the human mind did not allow us to remain content with the interpretation of the present state of the cosmical masses, but suggested the question—

What see'st thou else In the dark backward and abysm of time?

What was the original state of things? How had it come about that by the side of ageing worlds we had nebulae in a relatively younger stage? Had any of them received their birth from dark suns, which had collided into new life, and so belonged to a second or later generation of the heavenly bodies?

LOOKING BACKWARD.

During the short historic period there was no record of such an event; still it would seem to be only through the collision of dark suns, of which the number must be increasing, that a temporary rejuvenescence of the heavens was possible, and by such ebbings and flowings of stellar life that the inevitable end to which evolution in its apparently uncompensated progress was carrying us could, even for a little, be delayed. We could not refuse to admit as possible such an origin for nebulae. In considering, however, the formation of the existing nebulae we must bear in mind that, in the part of the heavens within our ken, the stars still in the early and middle stages of evolution exceeded greatly in number those which appeared to be in an advanced condition of condensation. Indeed, we found some stars which might be regarded as not far advanced beyond the nebular condition. It might be that the cosmical bodies which were still nebulous owed their later development to some conditions of the part of space where they occurred, such as conceivably a greater original homogeneity, in consequence of which condensation began less early. In other parts of space condensation might have been still further delayed, or even have not yet begun. If light matter were suggested by the spectrum of these nebulae, it might be asked further, as a pure speculation, whether in them we were witnessing possibly a later condensation of the light matter which had been left behind, at least in a relatively greater proportion, after the first growth of worlds into which the heavier matter condensed, though not without some entanglement of the lighter substances. The wide extent and great diffuseness of this bright-line nebulosity over a large part of the constellation of Orion might be regarded, perhaps, as pointing in this direction. The diffuse nebulous matter streaming round the Pleiades might possibly be another instance, though the character of its spectrum had not yet been ascertained.

THE MOTIONS OF THE STARS.

Besides its more direct use in the chemical analysis of the heavenly bodies, the spectroscope had given to us a great and unexpected power of advance along the lines of the older astronomy. In the future a higher value might, indeed, be placed upon this indirect use of the spectroscope than upon its chemical revelations. By no direct astronomical methods could motions of approach or of recession of the stars be even detected, much less could they be measured. A body coming directly toward us or going directly from us appeared to stand still. In the case of the stars we could receive no assistance from change of size or of brightness. The stars showed no true disks in our instruments, and the nearest of them was so far off that if it were approaching us at the rate of a hundred miles in a second of time, a whole century of such rapid approach would not do more than increase its brightness by the one-fortieth part. Still it was formerly only too clear that, so long as we were unable to ascertain directly those components of the stars' motions which lay in the line of sight, the speed and direction of the solar motion in space, and many of the great problems of the constitution of the heavens must have remained more or less imperfectly known. Now the spectroscope had placed in our hands this power, which, though so essential, had previously appeared almost in the nature of things to lie forever beyond our grasp; it enabled us to measure directly, and, under favorable circumstances, to within a mile per second, or even less, the speed of approach or of recession of a heavenly body. This method of observation had the great advantage for the astronomer of being independent of the distance of the moving body, and was, therefore, as applicable and as certain in the case of a body on the extreme confines of the visible universe, so long as it was bright enough, as in the case of a neighboring planet.

ALGOL AND SPICA.

By observations with the Potsdam spectograph, Professor Vogel found that the bright star of Algol pulsated backward and forward in the visual direction in a period corresponding to the known variation of its light. The explanation which had been suggested for the star's variability, that it was partially eclipsed at regular intervals of 68.8 hours by a dark companion large enough to cut off nearly five-sixths of its light, was, therefore, the true one. The dark companion, no longer able to hide itself by its obscureness, was brought out into the light of direct observation by means of its gravitational effects. Seventeen hours before minimum Algol was receding at the rate of about 241/2 miles a second, while seventeen hours after minimum it was found to be approaching with a speed of about 281/2 miles. From these data, together with those of the variation of its light, Vogel found, on the assumption that both stars have the same density, that the companion, nearly as large as the sun, but with about one-fourth his mass, revolved with a velocity of about fifty-five miles a second. The bright star of about twice the size and mass moved about the common center of gravity with the speed of about 26 miles a second. The system of the two stars, which were about 31/4 millions of miles apart, considered as a whole, was approaching us with a velocity of 2.4 miles a second. The great difference in luminosity of the two stars, not less than fifty times, suggested rather that they were in different stages of condensation, and dissimilar in density. It was obvious that if the orbit of a star with an obscure companion was inclined to the line of sight, the companion would pass above or below the bright star and produce no variation of its light. Such systems might be numerous in the heavens. In Vogel's photographs, Spica, which was not variable, by a small shifting of its lines revealed a backward and forward periodical pulsation due to orbital motion. As the pair whirled round their common center of gravity, the bright star was sometimes advancing, at others receding. They revolved in about four days, each star moving with a velocity of about 56 miles a second in an orbit probably nearly circular, and possessed a combined mass of rather more than two and one-half times that of the sun. Taking the most probable value for the star's parallax, the greatest angular separation of the stars would be far too small to be detected with the most powerful telescopes.

THE VALUE OF PHOTOGRAPHY.

Referring to the new and great power which modern photography had put into the hands of the astronomer, the president said that the modern silver bromide gelatine plate, except for its grained texture, met his needs at all points. It possessed extreme sensitiveness, it was always ready for use, it could be placed in any position, it could be exposed for hours, lastly it did not need immediate development, and for this reason could be exposed again to the same object on succeeding nights, so as to make up by several installments, as the weather might permit, the total time of exposure which was deemed necessary. Without the assistance of photography, however greatly the resources of genius might overcome the optical and mechanical difficulties of constructing large telescopes, the astronomer would have to depend in the last resource upon his eye. Now, we could not by the force of continued looking bring into view an object too feebly luminous to be seen at the first and keenest moment of vision. But the feeblest light which fell upon the plate was not lost, but taken in and stored up continuously. Each hour the plate gathered up 3,600 times the light energy which it received during the first second. It was by this power of accumulation that the photographic plate might be said to increase, almost without limit, though not in separating power, the optical means at the disposal of the astronomer for the discovery or the observation of faint objects.

TWO EXAMPLES.

Two principal directions might be pointed out in which photography was of great service to the astronomer. It enabled him within the comparatively short time of a single exposure to secure permanently with great exactness the relative positions of hundreds or even of thousands of stars, or the minute features of nebulae or other objects, or the phenomena of a passing eclipse, a task which by means of the eye and hand could only be accomplished, if done at all, after a very great expenditure of time and labor. Photography put it in the power of the astronomer to accomplish in the short span of his own life, and so enter into their fruition, great works which otherwise must have been passed on by him as a heritage of labor to succeeding generations. The second great service which photography rendered was not simply an aid to the powers the astronomer already possessed. On the contrary, the plate, by recording light waves which were both too small and too large to excite vision in the eye, brought him into a new region of knowledge, such as the infra-red and the ultra-violet parts of the spectrum, which must have remained forever unknown but for artificial help.

A PHOTOGRAPHIC CHART.

The present year would be memorable in astronomical history for the practical beginning of the photographic chart and catalogue of the heavens which took their origin in an international conference which met in Paris in 1887. The decisions of the conference in their final form provided for the construction of a great chart with exposures corresponding to forty minutes' exposure at Paris, which it was expected would reach down to stars of about the fourteenth magnitude. As each plate was to be limited to four square degrees, and as each star, to avoid possible errors, was to appear on two plates, over 22,000 photographs would be required. A second set of plates for a catalogue was to be taken, with a shorter exposure, which would give stars to the eleventh magnitude only. The plans were to be pushed on as actively a possible, though as far as might be practicable plates for the chart were to be taken concurrently. Photographing the plates for the catalogue was but the first step in this work, and only supplied the data for the elaborate measurements which would have to be made, which were, however, less laborious than would be required for a similar catalogue without the aid of photography.

A DELICATE OPERATION.

The determination of the distances of the fixed stars from the small apparent shift of their positions when viewed from widely separated positions of the earth in its orbit was one of the most refined operations of the observatory. The great precision with which this minute angular quantity, a fraction of a second only, had to be measured, was so delicate an operation with the ordinary micrometer, though, indeed, it was with this instrument that the classical observations of Sir Robert Ball were made, that a special instrument, in which the measures were made by moving the two halves of a divided object glass, known as a heliometer, had been pressed into this service, and quite recently, in the skillful hands of Dr. Gill and Dr. Elkin, had largely increased our knowledge in this direction. It was obvious that photography might be here of great service, if we could rely upon measurements of photographs of the same stars taken at suitable intervals of time. Professor Pritchard, to whom was due the honor of having opened this new path, aided by his assistants, had proved by elaborate investigations that measures for parallax might be safely made upon photographic plates, with, of course, the advantages of leisure and repetition; and he had already by this method determined the parallax for twenty-one stars with an accuracy not inferior to that of values previously obtained by purely astronomical methods.

PHOTOGRAPHIC REVELATIONS.

The remarkable successes of astronomical photography, which depended upon the plate's power of accumulation of a very feeble light acting continuously through an exposure of several hours, were worthy to be regarded as a new revelation. The first chapter opened when, in 1880, Dr. Henry Draper obtained a picture of the nebula of Orion; but a more important advance was made in 1883, when Dr. Common, by his photographs, brought to our knowledge details and extensions of this nebula hitherto unknown. A further disclosure took place in 1885, when the Brothers Henry showed for the first time in great detail the spiral nebulosity issuing from the bright star Maia of the Pleiades, and shortly afterward nebulous streams about the other stars of this group. In 1886 Mr. Roberts, by means of a photograph to which three hours' exposure had been given, showed the whole background of this group to be nebulous.

In the following year Mr. Roberts more than doubled for us the great extension of the nebular region which surrounds the trapezium in the constellation of Orion. By his photographs of the great nebula in Andromeda, he had shown the true significance of the dark canals which had been seen by the eye. They were in reality spaces between successive rings of bright matter, which appeared nearly straight, owing to the inclination in which they lay relatively to us. These bright rings surrounded an undefined central luminous mass. Recent photographs by Mr. Russell showed that the great rift in the Milky Way in Argus, which to the eye was void of stars, was in reality uniformly covered with them.

THE STORY OF THE HEAVENS.

The heavens were richly but very irregularly inwrought with stars. The brighter stars clustered into well known groups upon a background formed of an enlacement of streams and convoluted windings and intertwined spirals of fainter stars, which became richer and more intricate in the irregularly rifted zone of the Milky Way. We, who formed part of the emblazonry, could only see the design distorted and confused; here crowded, there scattered, at another place superposed. The groupings due to our position were mixed up with those which were real. Could we suppose that each luminous point had no relation to the others near it than the accidental neighborship of grains of sand upon the shore, or of particles of the wind-blown dust of the desert? Surely every star from Sirius and Vega down to each grain of the light dust of the Milky Way had its present place in the heavenly pattern from the slow evolving of its past. We saw a system of systems, for the broad features of clusters and streams and spiral windings marking the general design were reproduced in every part. The whole was in motion, each point shifting its position by miles every second, though from the august magnitude of their distances from us and from each other, it was only by the accumulated movements of years or of generations that some small changes of relative position revealed themselves.

THE WORK OF THE FUTURE.

The deciphering of this wonderfully intricate constitution of the heavens would be undoubtedly one of the chief astronomical works of the coming century. The primary task of the sun's motion in space, together with the motions of the brighter stars, had been already put well within our reach by the spectroscopic method of the measurement of star motions in the line of sight. Astronomy, the oldest of the sciences, had more than renewed her youth. At no time in the past had she been so bright with unbounded aspirations and hopes. Never were her temples so numerous, nor the crowd of her votaries so great.

The British Astronomical Association formed within the year numbered already about 600 members. Happy was the lot of those who were still on the eastern side of life's meridian! Already, alas! the original founders of the newer methods were falling out—Kirchhoff, Angstrom, D'Arrest, Secchi, Draper, Becquerel; but their places were more than filled; the pace of the race was gaining, but the goal was not and never would be in sight. Since the time of Newton our knowledge of the phenomena of nature had wonderfully increased, but man asked perhaps more earnestly now than in his days, what was the ultimate reality behind the reality of the perceptions? Were they only the pebbles of the beach with which we had been playing? Did not the ocean of ultimate reality and truth lie beyond?

* * * * *



CLIMATIC CHANGES IN THE SOUTHERN HEMISPHERE.

By C.A.M. TABER.

Having had occasion to cruise a considerable time over the Southern Ocean, I have had my attention directed to its prevailing winds and currents, and the way in which they affect its temperature, and also to the ice-worn appearance of its isolated lands.

It is now generally conceded that the lands situated in the high latitudes of the southern hemisphere have in the remote past been covered with ice sheets, similar to the lands which lie within the antarctic circle. The shores of Southern Chile, from latitude 40 deg. to Cape Horn, show convincing evidence of having been overrun by heavy glaciers, which scoured out the numerous deep channels that separate the Patagonian coast from its islands. The Falkland Islands and South Georgia abound with deep friths; New Zealand and Kerguelen Land also exhibit the same evidence of having been ice-laden regions; and it is said that the southern lands of Africa and Australia show that ice accumulated at one time to a considerable extent on their shores. At this date we find the southern ice sheets mostly confined to regions within the antarctic circle; still the lands of Chile, South Georgia, and New Zealand possess glaciers reaching the low lands, which are probably growing in bulk; for it appears that the antarctic cold is slowly on the increase, and the reasons for its increase are the same as the causes which brought about the frigid period which overran with ice all lands situated in the high southern latitudes.

Why there should be a slow increase of cold on this portion of the globe is because of the independent circulation of the waters of the Southern Ocean. The strong westerly winds of the southern latitudes are constantly blowing the surface waters of the sea from west to east around the globe. This causes an effectual barrier, which the warm tropical currents cannot penetrate to any great extent. For instance, the tropical waters of the high ocean levels, which lie abreast Brazil in the Atlantic and the east coast of Africa in the Indian Ocean, are not attracted far into the southern sea, because the surface waters of the latter sea are blown by the westerly winds from west to east around the globe. Consequently the tropical waters moving southward are turned away by the prevailing winds and currents from entering the Southern Ocean. Thus the ice is accumulating on its lands, and the temperature of its waters slowly falling through their contact with the increasing ice; and such conditions will continue until the lands of the high southern latitudes are again covered with glaciers, and a southern ice period perfected. But while this gathering of ice is being brought about, the antarctic continent, now nearly covered with an ice sheet, will, through the extension of glaciers out into its shallow waters, cover a larger area than now; for where the waters are shoal the growing glaciers, resting on a firm bottom, will advance into the sea, and this advancement will continue wherever the shallow waters extend. Especially will this be the case where the snowfall is great.

Under such conditions, it appears that the only extensive body of shallow water extending from the ice-clad southern continent is the shoal channel which separates the South Shetlands from Cape Horn, which is a region of great snowfall. Therefore, should the antarctic ice gain sufficient thickness to rest on the bottom of this shallow sea, it would move into the Cape Horn channel, and eventually close it. The ice growth would not be entirely from the southern continent, but also from lands in the region of Cape Horn. Thus the antarctic continent and South America would be connected by an isthmus of ice, and consequently the independent circulation of the Southern Ocean arrested. Hence it will be seen that the westerly winds, instead of blowing the surface waters of the Southern Ocean constantly around the globe, as they are known to do to-day, would instead blow the surface waters away from the easterly side of the ice-formed isthmus, which would cause a low sea level along its Atlantic side, and this low sea level would attract the tropical waters from their high level against Brazil well into the southern seas, and so wash the antarctic continent to the eastward of the South Shetlands.

The tropical waters thus attracted southward would be cooler than the tropical waters of to-day, owing to the great extension of cold in the southern latitudes. Still they would begin the slow process of raising the temperature of the Southern Ocean, and would in time melt the ice in all southern lands. Not only the Brazil currents would penetrate the southern seas, as we have shown, but also the waters from the high level of the tropical Indian Ocean which now pass down the Mozambique Channel would reach a much higher latitude than now.

The ice-made isthmus uniting South America to the antarctic continent would on account of its location be the last body of ice to melt from the southern hemisphere, it being situated to windward of the tropical currents and also in a region where the fall of snow is great; yet it would eventually melt away, and the independent circulation of the Southern Ocean again be established. But it would require a long time for ice sheets to again form on southern lands, because of the lack of icebergs to cool the southern waters. Still, their temperature would gradually lower with the exclusion of the tropical waters, and consequently ice would slowly gather on the antarctic lands.

The above theory thus briefly presented to account for the climatic changes of the high southern latitudes is in full accord with the simple workings of nature as carried on to-day; and it is probable that the formation of continents and oceans, as well as the earth's motions in its path around the sun, have met with little change since the cold era iced the lands of the high latitudes.

At an early age, previous to the appearance of frigid periods, the ocean waters of the high latitudes probably did not possess an independent circulation sufficient to lower the temperature so that glaciers could form. This may have been owing to the shallow sea bottom south of Cape Horn having been above the surface of the water, the channel having since been formed by a comparatively small change in the ocean's level. For, while considering this subject, it is well to keep in mind that whenever the western continent extended to the antarctic circle it prevented the independent circulation of the Southern Ocean waters, consequently during such times ice periods could not have occurred in the southern hemisphere.

It will be noticed that according to the views given above, the several theories which have been published to account for great climatic changes neglect to set forth the only efficacious methods through which nature works for conveying and withdrawing tropical heat sufficient to cause temperate and frigid periods in the high latitudes. While lack of space forbids an explanation of the causes which would perfect an ice period in the northern hemisphere, I will say that it could be mainly brought about through the independent circulation of the arctic waters, which now largely prevent the tropical waters of the North Atlantic from entering the arctic seas, thus causing the accumulation of ice sheets on Greenland. But before a northern ice period can be perfected, it seems that it will need to co-operate with a cold period in the southern hemisphere; and in order to have the ice of a northern frigid period melt away, it would require the assistance of a mild climate in the high southern latitudes.—Science.

* * * * *



AMMONIA.

In the majority of refrigerating and ice machines ammonia gas is the substance used for producing the refrigeration, although there are other machines in which other material is employed, one of these being anhydrous sulphurous acid, which is also a gas. Ammonia of itself is a colorless gas, but little more than one half as heavy as air. In its composition ammonia consists of two gases, nitrogen and hydrogen, in the proportion by weight of one part nitrogen and three parts hydrogen. The gas hydrogen is one of the constituents of water and is highly inflammable in the presence of air or oxygen, while the other component of ammonia, nitrogen, forms the bulk or about four-fifths of the atmosphere. Nitrogen by itself is an inert gas, colorless and uninflammable. Ammonia, although composed of more than three-fourths its weight of hydrogen, is not inflammable in air, on account of its combination with the nitrogen. This combination, it will be understood, is not a simple mixture, but the two gases are chemically combined, forming a new substance which has characteristics and properties entirely different from either of the gases entering into its composition when taken alone or when simply mixed together without chemical combustion. Ammonia cannot be produced by the direct combination of these elements, but it has been found that it is sometimes made or produced in a very extraordinary manner, which goes to show that there is yet considerable to be learned in regard to the chemistry of ammonia. Animal or vegetable substances when putrefying or suffering destructive distillation almost invariably give rise to an abundant production of this substance.

The common method for the manufacture of ammonia is to produce it from the salt known as sal-ammoniac. Sal-ammoniac as a crystal is obtained in various ways, principally from the ammoniacal liquor of gas works, also from the condensed products of the distillation of bones and other animal refuse in the preparation of animal charcoal, and which is of a highly alkaline nature. This liquid is then treated with a slight excess of muriatic acid to neutralize the free alkali, and at the same time the carbonates and sulphides are decomposed with the evolution of carbonic acid and sulphureted hydrogen. All animal matter, the meat, bones, etc., contain considerable carbon, while the nitrogen from which the ammonia is produced forms a smaller portion of the substance. The object is then to get rid of the carbon and sulphur, leaving the nitrogen to combine, through chemical affinity, with a portion of the hydrogen of the water, the oxygen which is set free going to form the carbonic acid by combining with the carbon. The liquor after being neutralized is evaporated to dryness, leaving a crystallized salt containing a portion of tarry matter.

The salt is then purified by sublimation, that is, it is heated in a closed iron vessel until it is transformed into a gas which separates and leaves, in a carbonized state, all foreign substance. After this gas is cooled, it condenses and again forms crystals which are in a much purer condition. If necessary to further purify it, it is again sublimed. The iron vessels in which the sublimation takes place are lined with clay and covered with lead. The clay lining and lead covering are necessary, for if the gas evolved during the process of sublimation came in contact with the iron surface, the gas would be contaminated and the iron corroded. Sublimed sal-ammoniac has a fibrous texture and is tough and difficult to powder. It has a sharp, salty taste and is soluble in two and a half parts of cold and in a much smaller quantity of hot water. During the process of sublimation the ammonia is not decomposed. But there are several ways in which the gas may be decomposed, and a certain portion of it is decomposed in the ordinary use of it in refrigerating machines. If electric sparks are passed through the gas, it suffers decomposition, the nitrogen and hydrogen then being in the condition of a simple mixture. When decomposed in this manner, the volume of the gas is doubled and the proportion is found to be three measures of hydrogen to one of nitrogen, while the weight of the two constituents is in the proportion of three parts hydrogen to fourteen of nitrogen.

The ammonia gas may also be decomposed by passing through a red hot tube, and the presence of heated iron causes a slight degree of decomposition. This sal-ammoniac is powdered and mixed with moist slaked lime and then gently heated in a flask, when a large quantity of gaseous ammonia is disengaged. The gas must be collected over mercury or by displacement. The gas thus produced has a strong, pungent odor, as can easily be determined by any one working around the ammonia ice or refrigerating machines, for as our friend, Otto Luhr, says, "It is the worst stuff I ever smelled in my life." The gas is highly alkaline and combines readily with acids, completely neutralizing them, and the aqua ammonia is one of the best substances to put on a place burned by sulphuric acid, as has been learned by those working with that substance, for although aqua ammonia of full strength is highly corrosive and of itself will blister the flesh, yet when used to neutralize the effect of a burn from sulphuric acid its great affinity for the acid prevents it from injuring the skin under such conditions.

The distilled gas, such as has just been described, is the anhydrous ammonia used in the compressor system of refrigeration, while it is the aqua ammonia that is used in the absorption system of refrigeration. Aqua ammonia or liquor ammonia is formed by dissolving the ammonia gas in water. One volume of water will dissolve seven hundred times its bulk of this gas, and is then known as aqua ammonia, in contradistinction to anhydrous ammonia, the latter designating term meaning without water, while the term aqua is the Latin word for water.

Anhydrous ammonia, the gas, may be reduced to the liquid form at ordinary temperatures when submitted to a pressure of about 95 pounds. During the process of liquefaction the ammonia gives up a large amount of heat, which if absorbed or radiated while the ammonia is in the liquid condition, the gas when allowed to expand will absorb from its surroundings an amount of heat equal to that radiated, producing a very great lowering of temperature. It is this principle that is utilized in refrigeration and ice making. In the absorption system, where aqua ammonia is used, the liquor is contained in a retort to which heat is applied by means of a steam coil, and a great part of the gas which was held in solution by the water is expelled, and carries with it a small amount of water or vapor. This passes into a separator in the top of a condenser, from which the water returns again to the retort, the ammonia gas, under considerable pressure, passing into the coolers. These are large receptacles in which the gas is permitted to expand. By such expansion heat is absorbed and the temperature of the surroundings is lowered. From the coolers the gas returns to the absorber, from which it is pumped, in liquid form, into the retort, to be again heated, the gas expelled and the process repeated. As the gas passes through the different processes, being heated under pressure, cooled, expanded again, more or less decomposition takes place, presumably from a combination of a small portion of the nitrogen with vegetable, animal, or mineral matter that finds its way into the system. Such decomposition, with the loss of nitrogen, leaves a small portion of free hydrogen, which is the gas that can be drawn from the top of the absorber, ignited and burned. The presence of hydrogen gas in the absorber is not necessarily detrimental to the effectiveness of the system, but as hydrogen does not possess the qualities of absorbing heat in the same way and to the same extent as ammonia, the presence of hydrogen makes the operation of the apparatus somewhat less efficient.—Stationary Engineer.

* * * * *

The refrigerating apparatus illustrated and described in the SCIENTIFIC AMERICAN SUPPLEMENT of June 25, No. 812, is substantially that patented by Messrs. Erny, Subers & Hoos, of Philadelphia. The illustration was copied from their patents of November and February last.

* * * * *

A NEW CATALOGUE OF VALUABLE PAPERS

Contained in SCIENTIFIC AMERICAN SUPPLEMENT during the past ten years, sent free of charge to any address. MUNN & CO., 361 Broadway, New York.

* * * * *

THE SCIENTIFIC AMERICAN

ARCHITECTS AND BUILDERS EDITION.

$2.50 a Year. Single Copies, 25 cts.

This is a Special Edition of the SCIENTIFIC AMERICAN, issued monthly—on the first day of the month. Each number contains about forty large quarto pages, equal to about two hundred ordinary book pages, forming, practically, a large and splendid MAGAZINE OF ARCHITECTURE, richly adorned with elegant plates in colors and with fine engravings, illustrating the most interesting examples of modern Architectural Construction and allied subjects.

A special feature is the presentation in each number of a variety of the latest and best plans for private residences, city and country, including those of very moderate cost as well as the more expensive. Drawings in perspective and in color are given, together with full Plans, Specifications, Costs, Bills of Estimate, and Sheets of Details.

No other building paper contains so many plans, details, and specifications regularly presented as the SCIENTIFIC AMERICAN. Hundreds of dwellings have already been erected on the various plans we have issued during the past year, and many others are in process of construction.

Architects, Builders, and Owners will find this work valuable in furnishing fresh and useful suggestions. All who contemplate building or improving homes, or erecting structures of any kind, have before them in this work an almost endless series of the latest and best examples from which to make selections, thus saving time and money.

Many other subjects, including Sewerage, Piping, Lighting, Warming, Ventilating, Decorating, Laying out of Grounds, etc., are illustrated. An extensive Compendium of Manufacturers' Announcements is also given, in which the most reliable and approved Building Materials, Goods, Machines, Tools, and Appliances are described and illustrated, with addresses of the makers, etc.

The fullness, richness, cheapness, and convenience of this work have won for it the LARGEST CIRCULATION of any Architectural publication in the world.

A Catalogue of valuable books on Architecture, Building, Carpentry, Masonry, Heating, Warming, Lighting, Ventilation, and all branches of industry pertaining to the art of Building, is supplied free of charge, sent to any address.

MUNN & CO., PUBLISHERS, 361 BROADWAY, NEW YORK.

* * * * *

BUILDING PLANS AND SPECIFICATIONS.

In connection with the publication of the BUILDING EDITION of the SCIENTIFIC AMERICAN, Messrs. Munn & Co. furnish plans and specifications for buildings of every kind, including Churches, Schools, Stores, Dwellings, Carriage Houses, Barns, etc.

In this work they are assisted by able and experienced architects. Full plans, details, and specifications for the various buildings illustrated in this paper can be supplied.

Those who contemplate building, or who wish to alter, improve, extend, or add to existing buildings, whether wings, porches, bay windows, or attic rooms, are invited to communicate with the undersigned. Our work extends to all parts of the country. Estimates, plans, and drawings promptly prepared. Terms moderate. Address

MUNN & CO., 361 BROADWAY, NEW YORK.

* * * * *

THE SCIENTIFIC AMERICAN SUPPLEMENT.

PUBLISHED WEEKLY.

Terms of Subscription, $5 a year.

Sent by mail, postage prepaid, to subscribers in any part of the United States or Canada. Six dollars a year, sent, prepaid, to any foreign country.

All the back numbers of THE SUPPLEMENT, from the commencement. January I, 1876, can be had. Price, 10 cents each.

All the back volumes of THE SUPPLEMENT can likewise be supplied. Two volumes are issued yearly. Price of each volume, $2.50 stitched in paper, or $3.50 bound in stiff covers.

COMBINED RATES.—One copy of SCIENTIFIC AMERICAN and one copy of SCIENTIFIC AMERICAN SUPPLEMENT, one year, postpaid, $7.00.

A liberal discount to booksellers, news agents, and canvassers.

MUNN & CO., PUBLISHERS, 361 BROADWAY, NEW YORK, N.Y.

* * * * *

USEFUL ENGINEERING BOOKS

Manufacturers, Agriculturists, Chemists, Engineers, Mechanics, Builders, men of leisure, and professional men, of all classes, need good books in the line of their respective callings. Our post office department permits the transmission of books through the mails at very small cost. A comprehensive catalogue of useful books by different authors, on more than fifty different subjects, has recently been published, for free circulation, at the office of this paper. Subjects classified with names of author. Persons desiring a copy have only to ask for it, and it will be mailed to them. Address,

MUNN & CO., 361 BROADWAY, NEW YORK.

* * * * *

PATENTS!

MESSRS. MUNN & CO., in connection with the publication of the SCIENTIFIC AMERICAN, continue to examine improvements, and to act as Solicitors of Patents for Inventors.

In this line of business they have had forty-five years' experience, and now have unequaled facilities for the preparation of Patent Drawings, Specifications, and the prosecution of Applications for Patents in the United States, Canada, and Foreign Countries. Messrs. Munn & Co. also attend to the preparation of Caveats, Copyrights for Books, Labels, Reissues, Assignments, and Reports on Infringements of Patents. All business intrusted to them is done with special care and promptness, on very reasonable terms.

A pamphlet sent free of charge, on application, containing full information about Patents and how to procure them; directions concerning Labels, Copyrights, Designs, Patents, Appeals, Reissues, Infringements, Assignments, Rejected Cases. Hints on the Sale of Patents, etc.

We also send, free of charge, a Synopsis of Foreign Patent Laws, showing the cost and method of securing patents in all the principal countries of the world.

MUNN & CO., SOLICITORS OF PATENTS, 361 Broadway, New York.

BRANCH OFFICES.—Nos. 622 and 624 F Street, Pacific Building, near 7th Street, Washington, D.C.

THE END