On the Variation of the Electrical Resistance of Glass, §c. 199 



* 4 On the Variation of the Electrical Resistance of Glass with 

 Temperature, Density, and Chemical Composition." By 

 Thomas Gray, B.Sc, F.R.S.E. Communicated by Pro- 

 fessor Sir William Thomson, F.R.S. Received December 

 28, 1881. Read January 12, 1882 * 



The following paper is a description of the methods adopted, and of 

 the results obtained, in a series of experiments on the specific resist- 

 ance of glass. These experiments were performed in the Physical 

 Laboratory of the Imperial College of Engineering, Tokio, Japan. 



An account of some preliminary experiments on this subject was 

 communicated by the author of this paper to the "Philosophical 

 Magazine" for October, 1880. In that paper attention was specially 

 directed to the change of resistance with change of temperature, and 

 to an apparently permanent change in electric quality which the 

 glass underwent when subjected to a high temperature. Subsequent 

 experiments have served to confirm the results there given, but show 

 that if the glass be newly made very little, if any, permanent change 

 is brought abou. by heating. 



In the experiments just referred to a current of electricity was 

 kept flowing either continuously or at short intervals during the 

 healing. As this might produce effects which would not be caused by 

 heating alone, it was thought desirable to test one or two specimens 

 for resistance at as low a temperature as possible, and then again, after 

 the glass had been heated to between 200° and 300° C, and cooled 

 to the same temperature. Experiments performed in this way have 

 shown an exactly similar change to that previously obtained. It 

 appears, therefore, that the change previously observed was due to 

 heating. 



The fact that the permanent change produced by heating to a high 

 temperature was markedly greater in specimens of old than in specimens 

 of new glass, rendered it probable that the change was due to some 

 previous change in the opposite direction, which goes on slowly at the 

 ordinary temperature. In order to put this conjecture to the test of 

 experiment, advantage ivas taken of several specimens of newly-manu- 

 factured glass which had just been obtained from the Government Glass 

 Works, Shinagawa, Tokio. The results of tests made on three speci- 

 mens of that glass are given in the following table. The first two 

 specimens were lime glass, while the third was a white semi- opaque 

 flint glass, containing arsenic. In the first column the number of the 

 specimen is written ; in the second the resistance in ohms between two 

 opposite faces of a cubic centimetre ; in the third, the temperature at 



* For abstract see ante, vol. 33, p. 256. 

 VOL. XXXIV. P 



