24 SirW. Thomson on the Thermoelastic, Thermomagnetic, 



P = «r(*-/Po) + ®(f-fo) +o-(y-yo + «-« +^- , 7o+?-fo); 



Q=w(?/-?/o) + ^-'7o) + "(^-^o + ^-^ + ?-? + ?-f ); 



K=«r(2:— ^o) + ®(?~?o) + o-(^ — ^o + y— y + f — f + ^~"^o)5 

 S=w(f — fo) + ©(« — ^o) + o"(y— y +« — «o + ^ _ ^o + ?— £o); 

 T==w(i7-i7o) + fi)(y-yo) + o-(^-^o + *-«o + ?-?o + f--fo)5 



u=OT(f-f )+ft)(^~^ )+o-(^-^o+y-yo+^-fo+ 7 7- ? ?o)- 



25. The three quantities, w, gj, cr, or the three coefficients of 

 elasticity according to the new system of independent variables, 

 will express, by their different relative values, the elastic pro- 

 perties of all crystals of the cubical class. For a perfectly iso- 

 tropic body, a particular numerical relation, which I have not 

 yet determined, must hold between ot, p, and cr ; and two inde- 

 pendent coefficients of elasticity will remain. To determine 

 this relation, and to find the formulae of transformation from 

 one set of variables to another on the new system, or from the 

 new system to the ordinary system (that which was used in the 

 preceding portion of this paper), or vice versa, may be interest- 

 ing objects of inquiry. 



Glasgow College, March 10, 1855. 



26. Extracted from, NichoVs i Cyclopaedia of the Physical 

 Sciences? second edition, 1860. Thermomagnetism: (1) Ex- 

 perimental Facts. — Gilbert found that if a piece of soft iron 

 between the poles of a magnet be raised to a bright red heat 

 it loses all its ordinary indications of magnetism, and it only 

 retains (Faraday, <Exp. Ees.' 2344-2347) slight traces of the 

 paramagnetic character. Nickel loses its magnetic inductive 

 capacity very rapidly as its temperature rises about 635° Fahr., 

 and has very little left at the temperature of boiling oil. 

 Cobalt loses its inductive capacity at a far higher temperature 

 than that of either, near the melting-point of copper. Of the 

 three metals, iron remains nearly constant, nickel falls gra- 

 dually, and cobalt actually rises in inductive capacity as the 

 temperature is raised from 0° to 300° Fahr. (Faraday, ' Exp. 

 Ees.' 3428 ; < Phil. Trans.' Nov. 1855). Cobalt, of course, 

 must have a maximum inductive capacity at some temperature 

 intermediate between 300° Fahr. and the temperature of melt- 

 ing copper. Crystals, when their temperatures are raised, 

 have their magnetic inductive capacities in different directions 

 of the crystalline substance rendered less unequal, and in 

 general to a very marked degree. Thus Faraday found the 

 difference of inductive capacities in different directions in 

 a crystal of bismuth (a diamagnetic crystal) reduced to less 

 than half when the temperature was raised from 100° to 280°, 



