78 



SCIENCE 



Vol. V., No. 103. 



of mathematics who would spend a couple of 

 hours in perusing it. 



The historical part of Abbott's ' Testing-ma- 

 chines ' is very brief, and consists of little more 

 than a catalogue of machines built and used in 

 the United States before the war. The second 

 part of the volume treats of the construction of 

 testing-machines, and the appliances used with 

 them. The author describes very fully and 

 clearly the apparatus made b}^ the Fairbanks 

 company, and much more briefly the machines 

 of Emery, Eiehle Brothers, Gill, and Olsen. 

 The remainder of the book relates to the use of 

 the testing-machine, and will be found a con- 

 venient handbook of instruction for beginners. 

 It points out certain precautions which must 

 be taken before and during a test ; speaks of 

 the appearance of the fracture as an indication 

 of quality ; shows what effect is produced upon 

 results by varying the size of the specimen, 

 the time of making the test, or the temperature 

 of the piece under examination ; and gives 

 several valuable tables. 



The author has apparently been very fortu- 

 nate in obtaining definite indications of the 

 ' elastic limit ' by a method which he describes 

 on pp. 84 and 138. As shown on his dia- 

 grams facing p. 82, this limit is indicated 

 by a sharp change in the direction of the ' stress 

 strain ' line, amounting to nearly 90°, shortly 

 followed b} r a sudden return of the line to its 

 original direction. 



These two points of inflection, occurring so 

 uniformly in an otherwise regular' curve, would 

 seem to point quite strongly to some pecul- 

 iarity of his apparatus. Indeed, we should 

 expect something of the sort in the use of a 

 testing-machine driven at a constant speed, as 

 soon as the test-piece begins to stretch faster 

 than the rate of the machine. The apparent 

 elastic limit obtained in this way would not 

 depend wholly upon the material tested, but 

 could be made to vary by changing the speed 

 of testing. 



Most of Winslow's little treatise on stadia 

 surveying is occupied by tables, — first, of 

 horizontal distances and differences of level, to 

 be used in the reduction of stadia field-obser- 

 vations ; and, second, of logarithms (to four 

 places of decimals) of sines and tangents, — 

 but is preceded by fcniyy-two pages devoted to 

 an exposition of the theory of stadia measure- 

 ments. This brief explanatoiy part would 

 have been more satisfactory if it had been re- 

 vised after its appearance in Van Nostrand's 

 engineering magazine, so as to obviate the 

 criticism which appeared in the number of the 

 same magazine for June of last year. 



In that paper it is shown, by Mr. R. S. 

 Woodward of the naval observatory, that the 

 formula expressing the relation between con- 

 jugate distances and the principal focal length 

 of a lens, or system of lenses, is exact if prop- 

 erly interpreted, and applies equally well to 

 any combination of lenses ; and that the ordi- 

 nary formula for the stadia instrument, if 

 properly understood, is exact, whatever may 

 be the number, kind, or disposition of the 

 telescope lenses, so long as they are properly 

 centred. This criticism, however, does not 

 affect Mr. Winslow's statement of the general 

 principles of stadia practice, but really con- 

 firms our belief in the superiority of stadia 

 measurement to ordinary chaining. The eight 

 pages of tables, previously used on the geo- 

 logical surve} T of Pennsylvania for reduction 

 of observations, we think will be found service- 

 able to engineers engaged in stadia work. 



Le Van's little book was prepared originally 

 as a series of articles for the Mechanical engi- 

 neer of New- York City. It has now been re- 

 vised, extended, and re-written to some extent, 

 for publication in its present form. It is an 

 elementary treatise upon the indicator, and 

 evidently intended solely for the class of readers 

 to which it was addressed at its first appear- 

 ance, — to those "whose education," as its 

 author says, "has been and must be rather 

 in the engine-room than in the class-room." 

 Its publication in the periodical for which it 

 was prepared is not a matter for public criti- 

 cism ; nor, perhaps, would be its presentation 

 in this later form, except for the fact that 

 the excellent work of Porter, its reproduction 

 with doubtful propriety by an American editor 

 and publisher, and the issue of the work of 

 Mr. Pra} r (another ' expert ' of unquestionable 

 practical experience and skill), have hardl} T 

 left a place for it. It lacks the precision of 

 the first, and the thoroughly practical charac- 

 ter of the other. 



We find no satisfactory description of the 

 familiar forms of instrument in the book. The 

 introductory part contains a misleading calcu- 

 lation of the gain in fuel by expansion, show- 

 ing an increase of economy which is never 

 reached in the best of engines, and never 

 even approximated in ordinary forms of the 

 motor. The explanation of the indicator dia- 

 gram, and the method of working it up, will 

 be useful, and will be most carefully studied by 

 the readers for whom the book is prepared. 

 The fact that its author is thoroughly familiar, 

 by practical use, with the instrument which he 

 describes, is evident throughout ; and this will 

 probably aid in securing for it a sale. 



