186 



SCIENCE 



[N. S. Vol. XXIX. No. 735 



requires ready familiarity witli other parts of 

 the book to make it available. 



This kind of treatment may be likened to 

 that used in the Euclidian geometry where a 

 separate demonstration is invented for each 

 proposition and few general methods are em- 

 ployed, a treatment in contrast with the de- 

 velopments of analytical geometry where 

 general laws and methods are applied to suc- 

 cessive cases or investigations. This kind of 

 treatment has many advantages from the 

 point of view of the practical man, while its 

 disadvantages are perhaps principally en- 

 countered by those who must at some period 

 of their career go somewhat more deeply into 

 theoretical questions. 



The contrast between the kinds of treat- 

 ment I have in mind will be clear to any one 

 who compares Grashof with Church. 



2. The diagrams employed by Church were, 

 I think, unique at the time his book was first 

 published, in their combined simplicity and 

 perspicacity. This arose, as I imagine, from 

 the way in which the book came into exist- 

 ence as a transcript of the author's black- 

 board lectures before his classes. Professor 

 Church had the opportunity while yet a young 

 man to devote himself to the single subject of 

 applied mechanics exempt from the distrac- 

 tions which usually beset college teachers of 

 that period of life who commonly have to 

 teach first one and then another subject. He 

 improved that opportunity to prepare this 

 text-book. It was an excellent thing to do, 

 and it was well done. It has stood the test 

 of prolonged use. No important or extensive 

 revision of the work has been undertaken by 

 the author until now, and even now its gen- 

 eral character and text has remained un- 

 changed. To make a rough estimate, possibly 

 100 pages scattered throughout the book have 

 been rewritten and replaced by a new or re- 

 vised text, leaving the paging unchanged of 

 so much of the original text as is retained. 

 It is needless to say that the emendations and 

 revisions have added greatly to the value of 

 the book by the introduction of much new 

 matter now necessary to the engineer, notably 

 concrete beams, circular ribs and hoops, thick 



hoUow cylinders and spheres. The most im- 

 portant matters thus added are in the more 

 abstruse parts of the subject, so that for the 

 ordinary student the most important addition 

 consists in the introduction of many valuable 

 illustrative examples, a change which will 

 meet general commendation. Indeed, the 

 book would be improved by the introduction 

 of still further examples. Another change, 

 apparently small, but of real importance, is 

 the adoption- of 1.41 for the ratio of the two 

 specific heats of gases instead of 4/3 used in 

 previous editions, following the example of 

 Weisbach. While 4/3 may be admissible as 

 a rough average for gases whose molecules 

 consist of three or more atoms, the gases the 

 engineer ordinarily deals with consist so 

 largely of diatomic molecules, especially air, 

 that there is no excuse for using a value dif- 

 fering from the experimental value for air,, 

 unless the gas to be treated be known to be 

 some polyatomic fluid, such as superheated 

 steam, carbonic acid, ammonia or the like. 



As a whole the book is singular for its clear, 

 lucid treatment, wise selection of subjects and 

 subordination of mathematical to mechanical 

 considerations. It has more definitely in view 

 the needs of the civil engineer than the me- 

 chanical or the electrical engineer. Indeed,, 

 the devotee of any of these branches of 

 engineering must expect ultimately to special- 

 ize to a far greater extent than is possible in 

 a general treatise like this. 



Henry T. Eddy 



Allen's Commercial Organic Analysis. Third 



edition. Vol. II., Part III. 



The volume in hand, which completes the 

 treatise, is chiefly devoted to the aromatic sub- 

 stances and to the essential oils, resins, etc. 

 The first part treats of the benzol derivatives 

 included under the following heads: Char- 

 acters and Classification of Aromatic Acids, 

 Benzoic Acid and Its Derivatives, Cinnamic 

 Acid and Its Derivatives, Salicylic Acid and 

 Its Allies, Dihydroxybenzoic Acids and Their 

 Allies, Gallic Acid and Its Allies, Phthalic 

 Acids. Special attention is paid to salicylic 

 acid, the detection and determination of which 



