of various Metals. 343 



plate of hard rubber in such a manner as to extend the arms 

 of the cross, which was then fastened to the rubber plate by 

 means of melted resin run between. Wires soldered to the 

 disks served for the connexions. 



The very considerable difficulty of soldering so thin a strip 

 of gold and then fastening it upon the plate has heretofore 

 prevented my employing this method of making connexions 

 with that metal, screw-clamps being used instead. The prac- 

 tical advantage of soldered connexions is of course consider- 

 able, though not so great as might at first appear. Resin, 

 although very brittle, was used as a cement, for the reason 

 that within the limits of temperature to be employed it is more 

 rigid than any other cement I could hit upon, and therefore 

 less liable to allow the gold strip to become distorted or strained 

 by the stress it is subjected to while carrying a current across 

 a powerful magnetic field. 



In order to control the temperature of the gold strip, it was 

 placed in a narrow tank between the poles of the electro- 

 magnet, and water was made to flow slowly through the tank, 

 from bottom to top, during the experiment. The lowest tem- 

 perature used was about 2° C, the highest about 30° C, as 

 will be seen below. 



August 2, the following results were obtained in the order 

 given : — 



Gold. 

 Temperature. Numbers proportional 



to transverse effect. 



30-2 C 1738 



2*2 1703 



2-6 1748 



30-0 1746 



No attempt was made to determine the absolute magnitude 

 of the rotational coefficient in this specimen of gold ; so that 

 the numbers given in the second column must not be used for 

 comparison with numbers elsewhere given as proportional to 

 the rotational coefficient in gold or other metals. 



The magnetic field in these experiments had an intensity of 

 about 1900 C-.Gr.S. The primary current was not measured 

 in absolute units. It was such as a Bunsen cell yields in a 

 circuit of a few ohms resistance. 



From the above table we get: — 



Temperature. Numbers proportional 



to transverse effect. 



30-2 1 «g- .... 17381 m „ 

 30-0 I 601 .... 1746 J 17iA 



2-21 2.4 • • • • 1703 "tl726 

 2-6/ /4 .... 1748 f iUb 



