172 ON FARADAY'S LIKES or FORCE. 



where 



and I, m. n are direction-cosines of a certain fixed line in space. 



The equations then become 



^p -my) T, 

 - no) T, 

 -l T. 



By the ordinary transformation of co-ordinates we may get rid of the 

 coefficients marked S. The equations then become 



where I', m', n' are the direction-cosines of the fixed line with reference to the 

 new axes. If we make 



dp dp dp 



a = - * = 



the equation of continuity 



da db dc _ 

 dx dy dz ~ 



becomes 



and if we make x 



d*P . d*p , d'p 



then :j+T7^+ jw=' 



dj? drf d 



the ordinary equation of conduction. 



It appears therefore that the distribution of pressures is not altered by 

 the existence of the coefficient T. Professor Thomson has shewn how to 

 conceive a substance in which this coefficient determines a property having 

 reference to an axis, which unlike the axes of P lt P t , P t is dipolar. 



For further information on the equations of conduction, see Professor 

 Stokes On the Conduction of Heat in Crystals (Cambridge and Dublin Math. 

 Journ.), and Professor Thomson On the Dynamical Theory of Heat, Part v. 

 (Transactions of Royal Society of Edinburgh, VoL xxi. Part i.). 



