138 



O. U. VONWILLER, 



0*06 gm. was applied near the free end, the distance between 

 rider and support being 5*3 cm. In one trial the depress- 

 ions of the free end observed at various times after the 

 first application of the load were : 



Time. Depression. 



40 seconds 0*1287 cm. 



• 80 „ 0*1330 „ 



190 „ 01377 „ 



495 „ 0-1460 „ 



while when the load was removed after being applied for 

 9 minutes, the recovery was as follows : 



Time. Recovery. 



40 seconds 0*1176 cm. 



120 „ 0*1286 „ 



180 „ 0*1322 „ 



315 „ 0*1384 „ 



The effect of light upon the continuous fall is shown in 

 Table I, where readings are given for several days during 

 the whole of which the load was applied. 



When the load was finally removed after being applied 

 for four days, the usual effects were observed, a rapid 

 initial recovery being followed by a gradual rise, which in 

 this case was still perceptible after 25 minutes. 



It is seen that the average fall per minute, given in the 

 fourth column, is invariably much greater for periods of 

 illumination than for those of darkness. When the room 

 was darkened after the selenium had been exposed to light, 

 the rate of fall did not drop suddenly but decreased gradu- 

 ally for several hours, as is seen clearly in the readings of 

 10th April. A corresponding lag occurs in the increase in 

 rate of fall when the selenium is illuminated after having 

 been in the dark, but this change is established in a much 

 shorter time than the other. It is very likely that the 

 viscosity varies with temperature changes, but it is certain 



