364 



O. U. VONWILLER. 



Cell 12, made 13th April, 1909. Wires 2\ mm. apart ; 

 length of wires in contact with selenium 2\ cms; average 

 thickness of selenium -h> mm., (determined by weighing 

 portions after the test had been carried out). In changing 

 the selenium to the conducting form the cell was heated 

 to 213° O. and cooled rapidly. The conductivity in the dark 

 at 18° 0. indicated a specific resistance of about one half 

 megohm. The source of light was an 8 c.p. lamp, and the 

 box was screened by a sheet of red glass and a water cell 

 in which the thickness of glass to be penetrated was 9 mm. 

 and that of water 11 mm. 



Table I. 

 Cell 12 — Conductivity in dark represented by 9-7 (mean value). 



Temper- 

 ature. 



Distance 

 of lamp. 



Added Conductivities. 



(£J+P a ) 



(Dx) 



(D 2 ) 



(V l +De) 



18°C. 



to 

 19°C. 



100 cms. 

 200 cms. 

 300 cms. 



2-81 

 1-60 

 1-08 



2-35 



1-42 

 0-90 



3-94 

 2-42 



1-70 



^ = •76 

 5-16 



2-42 



- -80 

 3-02 



198 



Cell 22, made 26th August, 1909. Wires 4J mm. apart, 

 length of wires in contact with selenium 3 cm. Thickness 

 not determined, as further tests are in progress with this 

 cell. The cell was heated three times to 190° C. and cooled 

 slowly each time. In the tests with red light the screens 

 were as described for cell 12; in the tests with "green " 

 light, a blue glass was used and a saturated solution of 

 copper sulphate used instead of the water. In the latter 

 case no red or yellow light could be detected after trans- 

 mission, a fairly bright band in the green and a little blue 

 and violet being seen when examined by a spectroscope. 



