—-s 
Saree Tee 
ne 2 ae Pe Ne 
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, 
irrespectively of 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withdrawn by them from his estimate of the enormous quantity 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 
Po Qo Ro 
its primary axis being that of x. Through a given point S, 
whose coordinates are x’, y’, 2’, conceive three surfaces confo- 
eal with A to be described, and let Pp, P’, Pp” 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 &, n, Z, and if we put 
P—P=Af, Pe — Pk’, p’ — py = kh", 
the equation of the surface A, referred to the new coordinates, 
will be 
E? 7? ty Eg non SoS i 
Sp he = (fy (A + 4 1), (2) 
where &o, no. 2) are the coordinates of its centre. 
