of mBthematk's who would spcod a couple of houra in peniBing it.
The historical part of Abbott's ' Teating-ma- chinea ' is very brief, and consists of little more Ibnn a catalogues of maciiines built and used in the United Slates before the war. The Bccond 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 by the Fairbanks company, and much more briefly the machines of Emery, Riehle Brolhera. Gill, and Olsen. The remainder of the book relates to the use of the testing-machine, and will be found a coo- venieDt 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 indiciition of quality; shows what effect is produced upon results by varying the size of the specimen, the time of making the test, or the tem[>erature of the piece under examination; and gives several valuable tables.
The author has apparently been verj' fortu- nate in obtaining definite iitdications of the ' elastic limit ' by a method which he describes on pp. 84 and 138. As shown on his dia- grams facing p. 82, thia limit is indicated by a sharp change in the direction of the ' stress strain' line, amounting to nearly 90°, shortly followed by a sudden return of the line to its original direction.
These two pointsof inflection, occurring so uniformly in an otherwise regular curve, would seem to point t]uite sti'ongly to some pecul- iarity of his apparatus. Indeed, we should expect something of the sort in the use of a testing- mad line driven at .t constant speed, as soon as the test-piece begins to stretch faster than the rate of the machine. The appareut elastic limit obtained in thia way would not depend wholly upon the material tested, but could l>e made to vary by changing the speed of testing.
Most of Winslow's little treatise on atadia surveying is occupied by tables, — first, of horizontal distances and differences of level, to be used in the reduction of stadia lield-obser' vationa; and, second, of logarithms (to four places of decimals) of sines and tangents, — but is preceded by forty-two pages devoted to an exposition of the theory of stadia measure- ments. This brief explanatory part would have been more satisfactory if it had been re- vised after its apt>earance in Van Nostrand'a engineering magazine, so as to obviate the criticism which appeared in the number of the same magazine for June of last year.
��Ill that paper it is shown, by Mr. R, Woodward of the naval observatory, that the formula expressing the relation between con- . ,iugate distancea and the principal focal length.! of a lens, or system of lenses, is exact if prop- I erly interpreted, and applies equally well to \ any combination of lenses; and that the ordl- narj- formula for the stadia instrument, properly understood, is exact, whatever may ( be the number, kind, or disposition of the 1 telescope lenses, so long as they are properly J centred. This criticism, however, does not 1 affect Mr. Winslow's statement of the general I principles of stadia practice, but really con- A firms our belief in the superiority of stadia J measurement to ordinary chaining. The eight T pages of tables, preriously used on the geo- 1 logical survey of Pennsylvania for reduction I of observations, we think will be found service- able to engineers engaged in stadia work.
Le Van's little book was prepared originally j as a aeries of articles for the Mechanical engi- j 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 uixin 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 ilaJ author says, "has been and must lie rather I 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 doublM propriety by an American editor and publisher, and the issue of the work of Mr. I'ray (another ' expert' of unquestionable practical experience and skill), have hardly J left a place for it. It lacks the precision of I the first, and the thoroughly practical charac- ter of the other.
We find no satisfactory description of the I familiar forms of instrument in the hook. The J introductory part contains a misleading calcn- latiou of the gain in fuel by expansion, ahow- ing an increase of economy which is never ] reached in the best of engines, and nc oven approximated in ordinary forma of the I motor. The explanation of the indicator dia- gram, and the method of working it np, will be useful, and will be most carefully studied by the readers for whom the book is prepared. The fact that ita author is thoroughly familiar, by practical use, with the instrument which he deaciibes, is evident throughout; and this will probably aid in securing for it a sale.
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