Ihe bitter iojufttice of the English writer and the calm impersonality of the American opti- cian, who was in the right, is skilfully woven into a tribute to 'follca's character. There follows a. short appreciative memoir of Mr. ToUes by Dr. George E. Blackham.
The remainder of Ibe volume is occu|}ied by the papers and proeeetlings, and contains ex- ceedingly little original matter. There arc articles which rqwat in detail perfectly familiar modes of work, and others which deal with those vague and worthless generalities of com- monplace which characterize half knowledge. Of the latter, the essay by Dr. J. Redding is a too perfect example. It is on the extra-vns- cuW circulation, and is largely formed of com- monplaces, the rest being half truths and total errors. For example : Dr. Redding says (pp. 85, 86). ■'■ Bile, gastric jnice, in fact all of the so-called secretions, together with the worn-out and etfete tissne-delritus, ai-e the result of physical disintegration of the outermost sub- stance of the cells." What can one do to help the anthor? Perhaps print the whole sen- tence in italics, to point out the {larts of it which are erroneons. We find, however, several articles of real interest. Some new appliances for convenient work are described. Gnndlach's suggestion of a new method of construction for olijcctives of low power, with increased angular 3|>ertnre, by changing the crown glass of an achromatic lens, and adapt- ing the flint glass to it. is noteworthy, and may lead to a valuable improvement. Attention sbould also be called to the very deserved criticism, by Edward Bausch, of the English 'society screw.' which is everything save a goo<l standard. It is much to be regretted that the volume contains so very little of results of original research.
��^ THURSTON'S METALLIC ALLOYS.
Is this volume are brouglit together the re- sults of the author's work' on metallic alloy's, with an introductory chapter on the history Mill characteristics of metals and their alloys, which is in the main the same as that to part ii,, and two chapters, one containing an enu- meration of the uses of the non-ferrous metals, and a statement of the location and reduction of their various ores ; and the other, iuterest-
��mtdallBf- By Prof. U.H.TUDBaT U't» p.. UluHr. »:
> Keponn of U.S. board lo teal USt. ind tuJ. IL. lUl.
��ing descriptions of the newer methods of work- ing hot and cold metals.
The scientific value of the experiments, whose record and discussion constitute the principal features of the book, and which were confined to the mechanical properties of com- mercial copper, tin, stiuc. and their alloys. — attention being chiefly given to tlie strength and elasticity of these alloys when sulijected to ten- sile, compressive, bending, and twisting forces, — is diminished by the failure to exercise due care in the preparation of the alloys. The need of great care in this matter is i-ccognized and emphasized by investigators, for most alloys exhibit phenomena of liquation ; that is, they tend, when melted and about to solidify, to aeiutrate into their constituent metals, or into several masses composed of different al- loys. S[)eciBl precautions with respect to purity of the metals, rate of cooling, oxida- tion, temperature during melting, frequency of agitation, etc., must therefore be taken, if the resultant solidified mass is lo be homoge- neous.
Professor Thurston is fhlly aware of this liability lo liquation; but on "assuming charge of a series of experiments on the char- acteristics of alloys, and an investigation of the laws of combination," the duly assigned him by the U.S. t>oard, we find him holding the following view of the work : —
"The intention in the work here to be de- scribed was, not to determine the character of chemically pure metals, melted, cast, and cooled with special precaution, but to ascer- tain the practical value of dbmmercial metals, as found in the markets of the United States, melted in the way that such alloys are pre- pared in every foundry for business purposes, and cast and otherwise treated in every respect as the brass-founder usually handles liis work : and to determine wh.il is the pr.iclical value to the brass-founder and to the constructor of commercial metals, treated in the ordinary manner, and without any special precaution or any jieculiar treatment,"
The book will be acceptable to the engineer- ing public : for, besides the author's own work, it contains the views and results of other investigators, extensive tables on the physical and mechanical properties of bronzes and brasses, and Bolley's compilation of the tech- nically useful alloys, the author increasing this rich collection sliU further by reci|)es from French and American sources. The deter- mination and topograph ical rej^reaentation of 'the strongest of the bronzes' will also be found of decided interest.
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