with Crystalline Selenium. 403 



The resistance of each of the wires (except the end ones) 

 with which the plates of selenium were provided was ap- 

 proximately ascertained in this way ; and, by deducting the 

 resistances of the junctions, the resistance of the intervening 

 selenium was also ascertained. 



A plate of selenium was provided with four platinum wires 

 0*5 centim. apart, annealed at 170° C. The resistances were 

 measured with + and — currents, and the means assumed to 

 be sufficiently near for the purpose. 



Between wires. Measured resistances. 



1 and 2 31 megohms. 



2 „ 3 162 „ 



3 „ 4 11 „ 



1 „ 3 174 „ 



2 „ 4 172 „ 



From these measurements the separate calculated resistances 

 are : — 



Junction Resistance of Resistance of selenium 



number. junction. between j unctions. 



2 . . . . 9*5 megohms ) 1KC1 -, 



o a.k i, r -L32 me ononis. 



6 . . . . 0*0 megonm J & 



This is an instance of high selenium resistance in the middle 

 and low resistance towards the ends in an otherwise appa- 

 rently homogeneous plate, and of low junction resistances. 

 The two junctions were made at the same time, in the same 

 manner, by melting the selenium upon the wires ; and yet one 

 of them has nearly twenty times the resistance of the other. 



A second plate of selenium, provided with six platinum 

 wires and annealed at 150° C, was measured with + and — 

 currents in the same way, mean values being taken. This 

 gave the following results : — 



Junction Resistance of Resistance of selenium 



number. of junction. between junctions. 



2 . . . . 429 megohms) 00 -, 



o A7Q & f 22 megohms. 



O ..... 4/3 „ I -JQ 



5 .... 428 „ f » 



In this plate, therefore, nearly all the resistance was situated 

 in the junctions, whilst the selenium offered a comparatively 

 small resistance, its conducting-power being much greater at 

 one end than- at the other. 



A third plate was provided with seven platinum wires 0*7 

 centim. apart, annealed at 205° 0. It showed electrically 

 more homogeneity of material and equality of junction resist- 

 ances. 



2D2 



