On an Alloy to be used as a Standard of Electrical Resistance. 107 
the theory is not complete till all facts not fundamental, and 
all laws, have been referred by mathematical calculation to 
the fewest possible fundamental facts. These principles have 
been admitted in physical astronomy, and belong equally to 
other departments of physical science. Hence if the hypothesis 
of the existence of the «ther as the sole source of physical 
power be true, the mathematical investigation of the motions of 
an elastic fluid become essential ; and the new principles of the 
application of partial differential equations to the determination 
of fluid motion, which I have proposed, will have the same 
relation to the future progress of theoretical physics, as the dis- 
covery by Newton of the principles of the application of differen- 
tials in dynamics had to the progress of physical astronomy. 
On account of the important applications those principles may 
eventually receive, I purpose, as soon as I shall be able, to bring 
them again under the notice of mathematicians. 
Cambridge Observatory, 
January 17, 1861. 
XVII. On an Alloy which may be used as a Standard of Electrical 
Resistance. By A. Matruizssen, Ph.D* 
tn expression of electrical resistances in the absolute 
measure proposed by Webert is, and probably will 
always remain, the best ; but its determination requires so much 
apparatus and room, as well as so much skill in manipulation, 
that it is placed beyond the means of most experimenters. 
I have therefore deemed it worth while to test some alloys, to 
see whether I should not be able to find one— 
I. Whose resistance will remain the same, whether it be made 
of absolutely pure or commercially pure metals; in other words, 
that such an alloy may be made by any chemist or assayer, and 
its conducting power will always be the same. 
II. That its conducting power will not be altered by the 
process of annealing. 
III, That its conducting power will not vary much with an 
increase or decrease of temperature. 
IV. That the alloy will not alter by exposure to the atmo- 
sphere. | 
The great difficulty in obtaining absolutely pure metals, 
together with the fact that the smallest traces of impurity 
materially increase the electrical resistance of most metals, pre- 
* Communicated by the Author. 
+ Pogg. Ann. vol. Ixxxu. p. 337, 
1 
