We are indebted to The London Engineer for the engraving and description.

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Some romances and exaggerations of which the Pitch Lake, at Trinidad, has been the subject, are corrected by Mr. Albert Cronise, of Rochester, N.Y. Its area, height and distance from the sea have been overestimated, and a volcanic action has been ascribed to it which does not really exist. It is one mile from the landing place, is 138 feet above the sea level, is irregular, approximately round, and has an area of 109 acres. Its surface is a few feet higher than the ground immediately around it, having been lifted up by the pressure from below. The material of the lake is solid to a depth of several feet, except in a few spots in the center, where it remains soft, but usually not hot or boiling. But as the condition of the softest part varies, it may be that it boils sometimes. The surface of the lake is marked by fissures two or three feet wide and slightly depressed spots, all of which are filled with rainwater. In going about one has to pick his way among the larger puddles and jump many of the smaller connecting streams. Each of the hundreds of irregular portions separated by this network of fissures is said to have a slow revolving motion upon a horizontal axis at right angles to a line from the center of the lake, the surface moving toward the circumference. This motion is supposed to be caused by the great daily change in temperature, often amounting to 80 deg., and an unequal upward motion of the mass below, increasing toward the center of the lake. A few patches of shallow earth lying on the pitch, and covered with bushes and small trees, are scattered over the surface of the lake.

* * * * *

The Gardeners' Chronicle announces that Mr. Fetisoff, an amateur horticulturist at Voronezh, Russia, has achieved what was believed to be impossible, the production of jet black roses. No details of the process have been received.

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Recent Books.

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ELECTRO-METALLURGY. Electric Smelting and Refining: The Extraction and Treatment of Metals by means of the Electric Current. Being the second edition of Elektro-Metallurgie by Dr. W. Borchers. Translated, with additions, by Walter G. McMillan. With 3 plates and numerous illustrations in the text. 8vo, cloth. 416 pages. London and New York, 1897 $6.50

ELECTRO-TECHNICAL SERIES. By Edwin J. Houston, Ph.D., and A.E. Kennelly, D.Sc. Ten volumes: Alternating Electric Currents, Electric Heating, Electro-Magnetism, Electricity in Electro-Therapeutics, Electric Arc Lighting, Electric Incandescent Lighting, Electric Motors, Electric Street Railways, Electric Telephony, Electric Telegraphy. Each $1.00

ENGINEERS. The Practical Management of Engines and Boilers, including Boiler Setting, Pumps, Injectors, Feed Water Heaters, Steam Engine Economy, Condensers, Indicators, Slide Valves, Safety Valves, Governors, Steam Gages, Incrustation and Corrosion, etc. A Practical Guide for Engineers and Firemen and Steam Users generally. By William B. Le Van. 12mo, cloth. 267 pages. 49 illustrations. 1897 $2.00

EXPERIMENTAL SCIENCE. By George M. Hopkins. This book treats on the various topics of Physics in a popular and practical way. It describes the apparatus in detail, and explains the experiments in full, so that teachers, students and others interested in Physics may readily make the apparatus without expense and perform the experiments without difficulty. The aim of the writer has been to render physical experimentation so simple and attractive as to induce both old and young to engage in it for pleasure and profit. A few simple arithmetical problems comprise all of the mathamatics of the book. Many new experiments are here described for the first time. It is the most thoroughly illustrated work over published on Experimental Physics. 840 pages. Over 790 illustrations. Seventeenth edition. Revised and enlarged. 8vo, cloth $4.00

EXPLOSIVES. Lectures on Explosives. A course of Lectures prepared especially as a Manual and Guide in the Laboratory of the United States Artillery School. By Willoughby Walke, First Lieut. Fifth United States Artillery. Second edition. Revised and enlarged. 8vo, cloth. 435 pages. New York, 1897 $4.00

FEEDS AND FEEDING. A Handbook for the Student and Stockman. By W.A. Henry. 8vo, cloth. 657 pages. 1898 $2.00

* * * * *

Our large Catalogue of American and Foreign Scientific and Technical Books, embracing more than Fifty different subjects, and containing 116 pages, will be mailed, free, to any address in the world.

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MUNN & CO., 361 BROADWAY, NEW YORK.

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A COMPLETE ELECTRICAL LIBRARY

BY PROF. T. O'CONOR SLOANE,

Comprising five books, as follows:

Arithmetic of Electricity, 138 pages $1.00 Electric Toy Making, 140 pages 1.00 How to Become a Successful Electrician, 189 pp. 1.00 Standard Electrical Dictionary, 682 pages 3.00 Electricity Simplified, 158 pages 1.00

—The above five books by Prof. Sloane may be purchased singly at the published prices, or the set complete, put up in a neat folding box, will be furnished to Scientific American readers at the special reduced price of FIVE DOLLARS. You save $2 by ordering the complete set. FIVE VOLUMES, 1,300 PAGES, AND OVER 450 ILLUSTRATIONS.

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We cannot permit the receipt of Sloane's Electrical Library to pass by without complimenting you upon the same. It is a most admirable work. Should be in the hands of all those who are interested in electricity.

PHILLIPS, ORMONDE & CO., Engineers. Melbourne, Victoria.

I was highly pleased with the copy of Sloane's Electrical Library, which arrived in good condition. It is one of the most valuable works I possess in my library. The use of the Roentgen Rays in my profession has stimulated my desire for electrical knowledge greatly, and I consider Sloane's "Electrical Dictionary" a first-class book of reference. I shall be pleased to recommend it to my colleagues in search of such a work. Yours truly,

P.J. CLENDINNIN, M.D., Hon. Medical Electrician to the Melbourne Hospital.

MUNN & CO., Publishers, New York.

* * * * *

JUST PUBLISHED.

Second Edition, Revised and much Enlarged.

Gas, Gasoline and Oil Engines

By GARDNER D. HISCOX, M.E.

The only American Book on the Subject.

This is a book designed for the general information of every one interested in this new and popular motive power, and its adaptation to the increasing demand for a cheap and easily managed motor requiring no licensed engineer.

The book treats of the theory and practice of Gas, Gasoline and Oil Engines, as designed and manufactured in the United States. It also contains chapters on Horseless Vehicles, Electric Lighting, Marine Propulsion, etc. Second Edition. Illustrated by 270 engravings. Revised and enlarged.

LARGE OCTAVO. 365 PAGES. PRICE $2.50.

* * * * *

CONTENTS.

Chapter I.—Introductory, Historical. Chapter II.—Theory of the Gas and Gasoline Engine. Chapter III.—Utilization of Heat and Efficiency in Gas Engines. Chapter IV.—Heat Efficiencies. Chapter V.—Retarded Combustion and Wall Cooling. Chapter VI.—Causes of Loss and Inefficiency in Explosive Motors. Chapter VII.—Economy of the Gas Engine for Electric Lighting. Chapter VIII.—The Material of Power in Explosive Engines, Gas, Petroleum Products and Acetylene Gas. Chapter IX.—Carbureters and Vapor Gas for Explosive Motors. Chapter X.—Cylinder Capacity of Gas and Gasoline Engines, Mufflers on Gas Engines. Chapter XI—Governors and Valve Gear. Chapter XII.—Igniters and Exploders, Hot, Tube and Electric. Chapter XIII.—Cylinder Lubrication. Chapter XIV—On the Management of Explosive Motors. Chapter XV.—The Measurement of Power by Prony Brakes, Dynamometers and Indicators, The Measurement of Speed, The Indicator and its Work, Vibrations of Buildings and Floors by the Running of Explosive Motors. Chapter XVI.—Explosive Engine Testing. Chapter XVII.—Various Types of Gas and Oil Engines, Marine and Vehicle Motors.—Chapter XVIII.—Various Types of Gas and Oil Engines. Marine and Vehicle Motors—Continued. Chapter XIX—United States Patents on Gas, Gasoline and Oil Engines and their Adjuncts—1875 to 1897 inclusive—List of the Manufacturers of Gas, Gasoline and Oil Engines in the United States, with their addresses.

* * * * *

A FEW EXTRACTS OF NOTICES FROM THE PRESS.

It is a very comprehensive and thoroughly up-to-date work.—American Machinist.

The subjects treated in this book are timely and interesting, as there is no doubt as to the increasing use of Gas, Gasoline and Oil Engines, particularly for small powers. It gives such general information on the construction, operation and care of these engines that should prove valuable to any one in need of such motors, as well as those already having them in use.—Machinery.

What an engineer says:

I beg to acknowledge receipt of your book on Gas, Gasoline and Oil Engines, by Hiscox, by registered mail. I am highly pleased with the book. It is the best on Oil Engines I have ever seen, is not intricate in the calculations, and the illustrations are excellent. Yours truly,

S. DALRYMPLE, Chief-engineer S.S. "Talune." Melbourne, Victoria.

MUNN & CO., Publishers, SCIENTIFIC AMERICAN OFFICE, 361 Broadway, New York.

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PATENTS!

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