218 Notices respecting New Books. 



the iron is entirely neglected, as it has been found by many 

 experimenters to be very small when the temperature is less 

 than 100° C. or so, 



Putting aside these considerations for the time being, the ex- 

 periment, imperfect as it is, seems to indicate that a large part 

 (about 80 per cent.**) of the energy involved in hysteresis is used 

 in heating the substance of iron ; that the speed with which 

 the cycle is performed has very little effect upon hysteresis, 

 that is within 28 and 400 complete periods per second ; that 

 soft iron takes in ^Jq sec. at least more than 70 per cent, of the 

 magnetization it would have when subjected to the field for hours. 



Two curves (fig. 28) are added, as calculated from Prof. 

 Ewing's papers f, one for very soft iron and the other for 

 tempered pianoforte steel. The curve for soft iron will be 

 seen to lie lower than the observed temperature in the pre- 

 sent experiment, and in the steel the heating is seen to be 

 more than six times that for soft iron. 



[A somewhat more accurate method of measuring this dis- 

 sipated energy has been thought of, and approved by Sir 

 William Thomson. It is hoped that the work will be under- 

 taken before long and more satisfactory results arrived at.] 



XXX. Notices respecting New Books. 

 Graphics, or the Art of Calculation by Drawing Lines, applied espe- 

 cially to Mechanical Engineering ; ivith an Atlas of Diagrams. 

 By Prof. P. H. Smith. Part I. (Longmans, 1889.) 

 rPHE author observes that " this book will not enable the student 

 -*- of Practical Mechanics to dispense with the use of other books 

 treating mechanics in the ordinary manner."' After reading his 

 work, we say that this witness is true. What, then, is the writer's 

 intention? "It [the book before us] is intended to enable those 

 who have a knowledge of elementary mechanics to advance that 

 knowledge to any degree of thoroughness they may find useful, and 

 to apply that knowledge to the everyday problems of engineering 

 science, without the aid of the more complicated portions of alge- 

 braic and trigonometrical Mathematics, or of the differential and 

 integral calculus. Many have no taste or faculty for this latter 

 sort of Mathematics ; others have not the time needed to keep them 

 au fait in its use ; and, again, it is undeniably true that the solu- 

 tion of many a problem becomes practicable in point of time and 

 ease by the graphic method which would be intolerably tedious and 

 difficult without its aid." We remember hearing, some eighteen 

 years since, Prof. Crofton explain some diagrams he had drawn in 

 illustration of a paper on the " Stresses in Warren and Lattice 



* Profs. Warburg and Honig, by calormietric method, find the directly 

 observed heat to be from 60 to 70 per cent, of the amoimt calculated 

 from hysteresis in bar-magnets. (Wied. Ami. 1883, p. 814) 



t Phil. Trans, part ii. 1885. The numbers for soft iron are taken from 

 p. 556, and those for the steel calculated from the diagram in fig. 16 of pi. 60. 



