Royal Society, 63 



the use of a discontinuous function, in the clearest light, that the 

 student may understand both what it is and how it is overcome. 

 .... I have also introduced some propositions on the geodetic 

 method of determining the Figure of the Earth, suggested by an 

 acquaintance with the circumstances of the Great Trigonometrical 

 Survey of India, and by the volume of the Ordnance Survey of 

 Great Britain and Ireland recently published by Lieut. -Colonel 

 James, R.E., Superintendent of the Ordnance Survey." The re- 

 searches of Mr. Hopkins and Professors Hennessy and Haughton 

 are also referred to. . As a specimen of some of the calculations in 

 this volume, interesting to the general reader, we may cite the 

 following: — "The increase in height of the sea-level at Karachi 

 above that at Cape Comorin, arising from the drawing of the waters 

 northwards by the Himmalayas, and in consequence of the deficiency 

 of attraction of the ocean =643 feet." 



VII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from vol. xix. p. 467.] 

 December 22, 1859. — Sir Benjamin C. Brodie, Bart., President, 

 in the Chair. 



THE following communications were read : — 

 " On the Electric Conducting Power of Alloys." By A. Mat- 

 thiessen, Ph.D. 



In this paper I have given the determinations of the electric con- 

 ducting power of upwards of 200 alloys, and have found that the 

 metals employed may be divided into two classes, viz. — 



A. Those metals which, when alloyed with each other, conduct 

 electricity in the ratio of their relative volumes. 



B. Those metals which, when alloyed with one of class A, or with 

 each other, do not conduct electricity in the ratio of their relative 

 volumes, but always less. 



The alloys may be divided into three groups ; viz. — 



1 . Those made of the metals of class A with each other. 



2. Those made of the metals of class A with those of class B. 



3. Those made of the metals of class B with each other. 



From the experiments described in the paper I have tried to deduce 

 the nature of alloys, and have arrived at the following conclusions : — 



A. That most alloys are only a solution of one metal in the other ; 

 for, — 



1. On looking at the curves belonging to the different groups, we 

 see that each group of alloys has a curve of a distinct and separate form. 

 Thus for the first we have nearly straight lines ; for the second, the 

 conducting power decreases always rapidly on the side of the metal 

 belonging to class B, and then turning, goes almost in a straight 

 line to the metal belonging to class A ; for the third group we find a 

 rapid decrement on both sides of the curve, and the turning-points 

 united by almost a straight line. 



2. On examining that part of the curve where the rapid decrement 



