May 29, 1896.] 



SCIENCE. 



815 



that he ' canuot conceive of the antipodes ' he 

 uses the word differently from Huxley in the 

 sentences he quotes, for Huxley only says that 

 he believes that something will be accomplished, 

 though he cannot conceive how. It happens 

 that J. S. Mill uses Professor Brooks' example 

 to explain the proper use of the word, writing 

 {Logic, n., p. 321): "Antipodes were really, 

 not ficticiously, inconceivable to our ancestors : 

 they are, indeed, conceivable to us." Every- 

 one will agree that conceivability in Professor 

 Brooks' sense is not a necessary condition of 

 truth, but this does not concern his subsequent 

 argument. 



Professor Brooks states in his last letter that 

 Aristotle held ' ' that our business in this world is 

 to learn all we can of the order of nature, leav- 

 ing to more lofty minds the attempt to find out 

 what it is that ' produces anything and makes it 

 what it is.' " Yet very curiously in his pre- 

 vious article to which he refers (Science N. S. , 

 Vol. I., p. 126) he wrote: "I should like to 

 see hung on the walls of every laboratory * * * 

 the older teaching of the Father of Zoology 

 [Aristotle] that the essence of a living thing 

 is not what it is made of, nor what it does, 

 but why it does it." Professor Brooks seems to 

 have proceeded from the ignoramus of his pre- 

 ceding paper to ignorabimus now, but he is not 

 justified in taking Aristotle with him. 



J. McKeen Cattell. 



Columbia University. 



SCIENTIFIC LITERATURE. 

 A Text-hooh of Gas Manufacture for Students: 



By John Hornby, F. S. C. 12mo, pp. 261 ; 



6 plates. London, 1896, Bell & Sons. New 



York, Macmillan & Co. , 66 Fifth Ave. $1. 50. 



A concise little book setting forth the chief 

 points in gas manufacture in a manner that 

 students can readily grasp has been a desidera- 

 tum. The manufacture of coal gas, with its at- 

 tendant by-products, is very extensively de- 

 veloped in England ; hence to that country we 

 look for excellent treatises on this subject, and 

 this ' Text-book ' meets the requirements. 



After a short consideration of the properties 

 and value of various coals for gas making, the 

 author discusses carbonization ; the construction 



and setting of retorts and furnaces ; the various 

 appliances usually found in the retort house ; 

 the effect of temperature on the quantity and 

 quality of the gas and on the by-products ; con- 

 densation of tar ; removal of ammonia and the 

 elimination of other impurities ; methods of 

 testing purity and illuminating power ; the 

 various problems incidental to the distribution 

 of gas to the consumers, and the construction 

 of meters and burners. In Chap. XX. , on the 

 Composition of Coal Gas, is shown the effect of 

 the various components of gas on its illumina- 

 ting power. 



The American reader will notice the slight 

 attention given to water gas. Very little of 

 this is used in England, it having been de- 

 veloped within the last fifteen years, while in 

 most cases the English coal-gas works, with 

 their plants for saving by-products, have been 

 established much longer. A short description 

 of the Lowe process, together with a plate, is 

 given. 



The author divides the water-gas process into 

 'continuous,' in which the reaction between 

 carbon and steam takes place in an externally 

 heated retort, and ' intermittent, ' in which the 

 carbon is raised to incandescence by an air 

 blast, and then steam is blown into the hot 

 mass. He adds that the continuous process has 

 not proved a success. But in this country the 

 term ' continuous ' is applied to those processes 

 in which a non-luminous water gas is made in 

 a generator and stored in a gasometer, being 

 afterwards carburetted in externally heated 

 retorts. Processes of this character, notably 

 that of Wilkinson, have proved very successful 

 here for large works. 



A short description of Peeble's gas-enriching 

 process is followed by a chapter on sulphate 

 of ammonia, which closes the book. 



The print and plates are excellent and the 

 illustrations are generally good, excepting two 

 indistinct views of mechanical charging and 

 drawing apparatus. Frank H. Thorp. 



Bepetitoriwm der Chemie : Dr. Carl Arnold, 

 Professor der Chemie an der Kongl. Tier- 

 arzlichen Hochschule zu Hannover. Siebente 

 Auflage, Verlag von Leopold Voss, Hamburg 

 und Leipzig. 1896. 



