C 436 ] 



LIV. Notices respecting New Books. 



The Testing of Materials of Construction. A Text-booh for the 

 Engineering Laboratory and a Collection of the Results of 

 Experiment. By William Cawthoenb Unwin, F.H.S., 

 M. Inst. C.E., Professor of Engineering at the Central Institution 

 of the City and Guilds of London Institute, formerly Professor 

 of Hydraulic and Mechanical Engineering at the Royal Indian 

 Engineering College. (London : Longmans, Green, and Co., 

 1888.) 



The present work is a treatise on the strength of materials .used 

 in construction, considered in connexion with the instruments and 

 methods by which the properties of materials are investigated 

 experimentally. 



The treatise consists of three parts. In the first, the mechanical 

 properties of materials are explained — that is, their elasticity and 

 plasticity, and the relations between stress and strain. In the 

 second, the apparatus used in the engineering laboratory is described. 

 Lastly, the third part contains a collection of the most complete 

 and trustworthy results of testing, of all the ordinary materials of 

 construction. 



After an introduction, which the reader will do well to reperuse 

 when he has gone through the whole work, the author devotes 

 three chapters to an explanation of the mechauical properties of 

 materials. His explanations here, and indeed throughout the 

 book, are lucid and can be readily followed even by those who 

 may not be in possession of very advanced mathematical knowledge. 

 Some of the deductions, however, which the author makes from 

 the experiments which he quotes do not seem to us to be quite 

 justifiable. "We find for instance on page 89 the statement, " Some 

 remarkable experiments of Colonel Maitland at Woolwich show 

 that, contrary to common prejudice, the ultimate elongation is 

 increased by very rapid loading." We do not think that Colonel 

 Maitland's experiments, which were made on bars of unhardened 

 steel only two inches in length, settle the question, especially as 

 we learn on page 291 that " M. Barba has stated that in rapid 

 testing, the resistance is somewhat greater and the elongation less 

 than in slow testing." We rather incline to the opinion that when 

 the length of the piece tested is large compared with the sectional 

 area, slow testing, if not too slow, will often produce a greater 

 ultimate elongation than very rapid testing. In the case of iron 

 and steel very slow testing will always produce less elongation 

 than rapid testing. Again, though M. Tresca observed with had 

 and other plastic metals that large plastic deformation was unac- 

 companied by any sensible change in the density, the reader should 

 not be allowed to infer, as he probably would, that there is no 

 sensible change in density accompanying large plastic deformations 

 of such metals as copper and iron. The density of copper may be 



