-SI Si 



-Effect of Mechanical Hardening 



-1 a a + 2(l+P<* 2 )?> 



W C ° S ± yo\** + 4(l+P«V 

 where P and are constants depending on the form of the 

 knife edge and varying inclination of the instantaneous axis to 

 the face of the pendulum. Such a variation, as has already 

 been recognized (Lndia Survey, Pendulum Operations: Coast 

 Survey Keport, 1876), is detected by a non-periodic acceleration 

 on of rate. 



Art. XXI— On the Effect of Mechanical Hardening on the 

 Magnetic Properties of Steel and Iron ; by Louis M. 

 Cheesman* 



1. Introduction. — The relation between the magnetism and 

 hardness of steel and iron has for many years been a subject of 

 scientific investigation, and especially in the last few years 

 many valuable results have been obtained in this connection. 



These investigations, however, have been almost ex< 

 confined to the effect of the hardness brought about in steel and 

 iron by the action of heat, while that which is caused by me- 

 chanical means has been left for the most part unconsidered. 

 This is the more remarkable as the fact, that the mechanical 

 bardei mg exerts an influence on the capacity to retain magnet- 

 ism, has certainly been known for nearly a century. Cou- 

 lomb, f who I believe was the first to publish this fact, says, in 

 of increasing the magnetic capacity by means of 

 ig, that " the hardness does not need to be accomplished 

 ig to redness and then suddenly cooling, but that a 

 mechanical hardening as well causes an increase in the perma- 

 nent magnetic moment." 



In this connection should also be mentioned an iir 

 by Airy 4 who informs us that the magnetism assumed by cold- 

 and hot-rolled iron, under similar cTrc 



other as 6" is to 5. Lastly I would refer 



L . ioiii ^< voi, . ttl„ T< v >e find it st it.-d that tin caj ;i<-it\ ^ 

 soft iron for induction is materially altered bv a mcchaniea! 

 hardening. Thus, although the subjeel under 'consideration is 

 bv no means a new one, still little. 'if anything, beyond what 

 h;is already been stated, seems to be known in regard to it ; and 

 I have therefore endeavored, at the instigation of Prof. F. 



f Coulomb, mem. del'Aead v(<\ <U-< s i« ls < <•- p j..., itm Wied. Galv., II. a ; 



I'i^ysi 



mts on Iron Built Ships. Philos. Trans. 

 Lamont'sHandbuch dea Magnetismus, p. 255. 



