68 Scientific Intelligence. 



found to increase, gradually at a rate diminishing continuously 

 through infinite time — diminishing very slowly in case of low 

 temperatures «100°), very rapidly at first and then again slowly 

 in case of high temperature (^> 200°) ; so that the highest and 

 hardest of the inferior states of hardness possible at any temper- 

 ature is approached asymptotically. The observed law that 

 thermo-electric power and specific resistance are linear functions of 

 each other, suggests the introduction of the new variable thermo- 

 electric hardness, which is used as the measure of hardness 

 throughout the work. In chapter III, finally, the attempt is 

 made to throw new light on the laws set forth in chapter II, by 

 following them into their ulterior consequences. With the aid of 

 certain allied electrical properties observed in alloys of silver and 

 in malleable cast iron, the nature of the phenomenon of hardness 

 as presented by steel is discussed from every physical and chem- 

 ical point of. view, within the scope of the memoir. 



With these results in hand the authors commence the study of 

 the subject proper of the research, the magnetic behavior of tem- 

 pered steel. An introductory chapter, IV, determines the value 

 and relations of the thermo-electric effect of magnetization. Chap- 

 ter V then exhibits with some detail, the effect of hardness on 

 the maximum of magnetization which thin cylindrical steel rods 

 of different dimensions permanently retain. The method for the 

 accurate definition of hardness and the scheme of operations for 

 tempering developed in chapter II, are here rigidly adhered to ; 

 the magnetic results reached are therefore sharp and consistent. 

 Chapter VI investigates the bearing of temper on the condition of 

 magnetic stability of steel. Whenever great retentiveness, both 

 as regards the hurtful effects of temperature and time and shocks 

 is to be conveniently attained with the least sacrifice of magneti- 

 zation, magnets should be treated thus : 



1. Having tempered the steel rod uniformly, expose it for a- 

 long time (20 to 50 hours) to the annealing effect of steam. The 

 operation may be interrupted as often as desirable. The magnet 

 will then exhibit the maximum of permanent hardness for 100°. 



2. Magnetize the rod and again expose it for some time (5 to 

 10 hours) to the annealing effect of steam. The operation may 

 be often interrupted. The magnet will then exhibit both the 

 maximum of permanent magnetization as well as the maximum 

 of permanent hardness for 100°. It will show exceptional reten- 

 tiveness at ordinary temperature. 



Finally in chapter VII, the authors endeavour to generalize 

 on the foregoing results as a whole; to re-state the principal facts 

 with greater accuracy and breadth of scope than was possible in 

 the earlier chapters, to deduce from all a method for the physical 

 definition of iron-carburets. They find, in particular, that the dif- 

 ference between the logarithms of the extreme values of thermo- 

 electric hardness for the same carburation, passes through a 

 pronounced maximum, defining a carbide the mechanical proper- 

 ties of which are those of a type steel. 



