Resistance and other Properties of Sulphur. 



145 





Scale 

 deflection 



at the 

 beginning. 



Til-no 



.Lime. 



Fall in scale 

 divisions. 



otate. 







minutes. 







1st scries (lj . 



1 sn 



OA 



oU 



on 



.uarK. 





J> 



19 



OC\ 



-L/lgllt;. 



(3) . 





35 



18 



Park. 



^5nci series (4) . 





ID 



OK 



Light. 







J. / 



OK 





>) 



1 K 

 xo 



OC\ 



JjaiJi. 



IO- 





lo 



1 Q 





CS). 



>) 



15 



20 



Light. 



3rd series (9) . 



200 



15 



14 



Light. 



5> 



(10) 





15 



17 



(11) 





16 5 



16 





(12) 





15 



10 



Dark. 



(13) 





15 



10 



55 



The first and second series were alternated dark and. light in the 

 same set of experiments to see that no permanent change was pro- 

 duced and mistaken for the effect sought. In the first the time varied 

 and the deflections were allowed to fall the same distance ; in all the 

 others the time was the same and the fall varied. 



The method of performing the experiments made it possible that the 

 effect might be produced by the heat of the sun and not by the light. 

 The variation in temperature observed on a delicate thermometer was 

 about 1° C. To eliminate the effect of heat, a long series of observa- 

 tions was made in the dark, whilst the temperature was raised slightly 

 by placing a Bunsen flame 4 or 5 inches away from the screen pro- 

 tecting the sulphur, and the heat radiated by placing an iron spiral 

 in it, then one of copper, and lastly a fine clay tile. 



The range of temperature was 15*2° C. to 17*1° C. in the first ten 

 experiments, in which the heated ones fell rather more slowly than 

 those at a lower temperature. In the next seven observations the 

 range was 14'8° C. to 18° C, the fall being exactly the same in each. 



There yet remained the possibility that the light falling on the 

 wires which held the rods caused the charge to escape more quickly 

 into the air. When, however, the sulphur was removed, the effect 

 produced by the light on the portions of wire exposed to its influence 

 was too small to produce any change in the rate of fall. 



Hence it appears that although selenium is the body most sensitive 

 to the action of light, it shares its property with its neighbours, and 

 the three elements (constituting the same group), sulphur, selenium, 

 and tellurium, are all similarly acted upon, furnishing another example 



VOL- XLVI. L 



