Chemistry and Physics. 301 
slum took place under a moderately high column of saturated 
water, the pressure exercised by this column would give a satis- 
factory explanation for the fact that calcic sulphate crystallized 
cables, I was induced to experiment with bars of selenium, a 
tying in length from 5 to 10 centimeters, and of a diameter from 
jected. When the bars were fixed in a box with a sliding cover, 
S0 as to exclude all light, their resistance was at its highest, and 
remained very constant, fulfilling all the conditions necessary to 
equi immediately the 
* Communicated to the Society of Telegraph Engineers, February 12, by Mr° 
on Clark, from Mr. Willoughby Smith, Electrician to the Telegraph Construc- 
mpany. 
. 
