142 O. U. VONWILLER. 



made to produce threads of the substance in this form. 

 Considerable difficulty was met, but a few satisfactory 

 preparations were made by placing threads of vitreous 

 selenium on a horizontal sheet of mica in a closed heating 

 oven, the temperature of which was slowly raised to about 

 180° 0., the time occupied in the heating being about two 

 hours. Generally after the heating the thread was found 

 to be broken into very short lengths, but several good 

 pieces were obtained. Very great care was needed in 

 handling these preparations as they are extremely fragile 

 and threads were frequently broken before any satisfactory 

 readings were obtained. 



As with the vitreous selenium, it was found that the 

 application of a load to the end of a "beam" of crystalline 

 selenium resulted in an immediate elastic depression 

 followed by a gradual fall with continued application of 

 the load; this gradual fall, however, in all cases was much 

 smaller than with vitreous selenium under corresponding 

 conditions. The viscosity effect is much greater shortly 

 after removal of the thread from the heating oven, decreas- 

 ing for several hours. A few observations were made with 

 threads prepared at different temperatures, ranging from 

 179° O. to 197° C, but it is impossible to say, from them, 

 how the effects depend on the temperature of preparation. 



With crystalline selenium light appears to have no 

 influence on the immediate elastic depression due to load- 

 ing and it has been impossible to detect any difference, due 

 to change of illumination, in the rate of movement under 

 continued application of a load. However, as the rate of 

 movement was always very small and as the threads broke 

 before a long series of readings could be made, the failure 

 to detect a light effect on the viscosity of crystalline 

 selenium must not be taken as conclusive evidence that it 

 does not exist or even that it is very small. 



