429 



In order to discover how far the experiment supports either 

 of these positions, Mr. Donovan adduced counter-experiments, 

 in which combinations of zinc and copper were acted on by di- 

 lute acid of different strengths until dissolved. The solution 

 took place in different periods of time, and, consequently, the 

 electricity evolved during any given period was unequal in 

 quantity, in some cases very much so ; yet in all of them the 

 effect on the galvanometer was the same. 



These experiments appear incompatible with Faraday's law 

 of equal quantities of electricity producing equal deflections, 

 irrespectivelyof other circumstances. Support is, consequently, 

 withdrawn by them from his estimate of the enormous quantity 

 of electricity naturally associated with matter. 



The following note by Professor Mac Cullagh was read. 

 Let a surface A of the second order be represented by the 

 equation 



^+^+5^ = 1, 

 Po Qo Ro 



its primary axis being that of re. Through a given point S, 

 whose coordinates are x', y', z', conceive three surfaces confo- 

 cal with A to be described, and let p, p', v" be the squares of 

 their primary semiaxes. Then, if normals drawn to these sur- 

 faces respectively at the point S be the axes of a new system 

 of coordinates ?, jj, ?, and if we put 



p — Po = A, p' — Po = k', v" — Po = k", 



~,/2 ,/2 y2 



Po Qo Ro '^ 



the equation of the surface A, referred to the new coordinates, 

 will be 



where ^oj »Jo5 So ^rc the coordinates of its centre. 



