On the Measurement of Small Resistances. 



291 



merits are now proceeding with cells of this kind varying in 

 length from two to eight inches. 



(8) The theorems enunciated above concerning the advan- 

 tages of enlarging the size of the selenium-cell can readily 

 be put to experimental test with cells such as described. 

 There is of course a practical limit beyond which further 

 increase of size will be of no advantage — such a limit being 

 determined in particular cases by the resistance of the tele- 

 phones and of the telephone-circuit, and by the other condi- 

 tions, electrical and optical, of the experiment. 



Universitv College, Bristol, 

 Nov. 24, 1880. 



XXXIX. On the Measurement of Small Resistances. By R. T. 

 Glazebrook, M.A., Fellow of Trinity College, and Demon- 

 strator of Experimental Physics at the Cavendish Laboratory, 

 Cambridge*. 



WHILE measuring some small resistances with a Wheat- 

 stone's bridge at the Cavendish Laboratory, Mr. W. 

 B. Allcock observed that the apparent measure of the resis- 

 tance varied with the resistance in the battery circuit. 



Let A D C be the bridge-wire, D being the point at which 



— !■!■ — - 



the sliding contact is to be made. Let P be the resistance 



* Communicated by the Physical Society, having been read at the 

 Meeting- on January 22, 1881 . 



