Rowland — Studies on Magn 



: Distribution. 



long. One of tbese halves was hardened till it could scarcely 

 be scratched by a file, but the other half was left unaltered. 

 The following table gives the distribution, using the same unit 

 as that of Tables XIII. and XIV. The bars were so short that 

 the results can hardly be relied on ; but they will at least 

 suffice to show the change. 



In fig. 7 I 

 )m Table 



have attempted to give the curve of distribution 

 XV, and have made the curves coincide with 

 observation as nearly as pos- 

 '• sible, making a small allow- 



ance, however, for the errors 

 introduced by the shortness of 

 the bar. It is seen that the 

 effect of hardening in a bar of 

 these dimensions is to increase 

 the quantity of magnetism, but 

 especially that near the end. 

 Had the bar been very long^ no in- 

 crease in the total quantity of 

 magnetism woxdd have taken 

 place^ but the distribution would 

 have been changed. Hence from 

 this we deduce the important 

 fact thai hardening is most useful 

 for short magnets. A nd it would 

 seem that almost the only use in 

 hardening magnets at all is to 

 concentrate the magnetism and 

 to reduce the weight. And in- 

 deed I have made magnets 

 hose magnetization at the central section was 

 s in a steel wire of the same size ; but to all 

 less strongly magnetized than the steel be- 

 ; diffused ; and as the magnetism 

 the steel, its 



It is for these reasons that many makers of surveyors' com- 

 passes find it unnecessary to harden the needles, seeing that 

 these are long and thin. 



We might deduce all these facts from the formulae on the 

 assumption that r is greater, the harder the iron or steel. 



Having thus considered briefly the distribution on electro- 

 magnets and steel magnets, and found that the formulae repre- 

 sent it in a general way, we may now use them for solving a 

 few questions that we desire to know, though only in an 

 approximate manner. 



[To be continued] 



just a 

 appea] 

 cause the magnetism 



