922 



SCIENCE. 



[N. S. Vol. V. No. 128. 



several parts is 86, 215, 167 and 254, the re- 

 maining 65 pages being devoted to an appendix 

 and index. Although mainly designed for en- 

 gineers, it will be useful to physicists and to all 

 who have to do with the mechanic arts, for a 

 large part of the information that it gives can 

 be found in no other book. The task of the 

 author in sifting and discussing the vast number 

 of tests on record was a difficult one, but it has 

 been performed with skill and success. 



Part I is somewhat disappointing in that it is, 

 in the main, occupied with elementary matter 

 regarding bars and beams which is found in all 

 text-books on the resistance of materials. In 

 an advanced work of this kind the engineer or 

 physicist would naturally expect to find the 

 mathematical theory of elasticity developed to 

 a point in advance of that taught in technical 

 schools, and especially to see the theory of true 

 internal stress in beams set forth. A valuable 

 discussion regarding the elastic limit is here 

 given, and the results of very recent theoretic 

 in^'estigations of combined concrete and iron 

 beams are presented. 



Part II, although perhaps giving a fuller ac- 

 count of the manufacture and properties of ma- 

 terials than other general works on construc- 

 tion, has not been prepared with the best care 

 and discrimination. For instance, the blast 

 furnace is not mentioned, although 14 pages on 

 the manufacture of cast Iron is quoted from a 

 British book on metallurgy. The chapter on 

 timber, which fills 97 pages, is a reprint from 

 a bulletin of the United States Forestry Bureau, 

 and much of this might have been well omitted 

 altogether, while the remainder should have 

 been properly digested and condensed. Steel, 

 cement and paving brick are discussed, how- 

 ever, in a very clear and concise manner. 



Part III presents a more complete account of 

 testing machines and methods of testing than 

 can be found elsewhere in book form. The 

 classification and discussions are here most ex- 

 cellent, and the presentation of conclusions of 

 the European commissions on the question of 

 standard specimens and methods is very com- 

 plete. Static tests of tension and flexure nat- 

 urally receive the greatest share of attention. 

 Impact tests, with the exception of the cold- 

 bend and drifting methods, seem inadequately 



treated in view of their growing use and im-. 

 portance ; for instance, the flexural test of steel 

 rails by a falling ram, where deflections and the 

 elongations on the tensile side are measured, 

 has long been used in Europe and during the 

 past five years has been adopted by some of our 

 leading railroads, and hence should have re- 

 ceived at least brief notice. 



Part IV gives an admirable digest of the re- 

 sults of experiments on materials. A most ex- 

 cellent feature, and one which indeed runs 

 throughout the entire book, is the presentation 

 of results by means of diagrams. These set 

 forth the relations between the different proper- 

 ties of materials far more clearly than columns 

 of figures can do and enable the reader to make 

 comparisons which otherwise would be difficult 

 or impossible for him to undertake. The tests 

 which are discussed are, in the main, those pre- 

 cise and comprehensive ones made on metals 

 during the past twenty years by Bauschinger, 

 Tetmajer, the French commission, and by How- 

 ard at the Watertown arsenal, and those by the 

 author on timber. Lack of space forbids a 

 mention of the conclusions and results here re- 

 corded, but it should be said that the care exer- 

 cised in selecting the data and the admirable 

 method of presentation is alone sufficient to 

 render the book an authoritative one. 



The proper definition of the term ' elastic 

 limit ' has long been a puzzling question. 

 While generally defined as the limit at which 

 Hooke's law of proportionality of stress to de- 

 formation fails to hold good, it has also been 

 explained to be characterized by the beginning 

 of the permanent set, while in commercial tests 

 the so-called yield point, where a sudden mo- 

 lecular change occurs, is generally regarded as 

 the elastic limit. The author discusses these 

 definitions at length, and proposes that the 

 term ' apparent elastic limit ' be used to indi- 

 cate that point where the rate of elongation is 

 fifty per cent, greater than the rate at the be- 

 ginning of the elongation. This definition en- 

 ables the elastic limit to be readily marked on a 

 stress diagram, and for ductile materials it ap- 

 pears to locate a characteristic point which lies 

 higher than the limit of elastic proportionality 

 and lower than the yield point. The new 

 definition, although defective in not referring 



