( 812 ) 



If the plate is again removed, the deflection decreases again to 

 the value it had before the plate was placed between etc. So this 

 fully proves that it is the radiation of light which influences the 

 conductivity of* antimonite in so high a degree, and not the heak 

 for the latter diminishes the conductivity, in contrast with the former. 



§6. Finally glass plates of different colours were interposed between 

 the source of light and the rod. 



It then appeared that the influence of the differently coloured 

 light was very different. The antimonite namely proved to be subjected 

 to hardly any change by green light; for red light the increase was 

 pretty large, for yellow light a little more, for green very small, 

 for violet light again stronger. In each of these cases the deflection 

 appeared to have resumed its original value after removal of the 

 source of light 1 )- With violet radiation I obtained an increase ot 

 conductivity which amounted to about 150 % of the original value; 

 with white light with interposed glass plate one of about 250 °/ . 



To get some insight into the quantitative action for a special case, 

 the following experiments were made. An ordinary electrical incan- 

 descent lamp was adjusted at 1(5 cms', distance from an antimonite rod 

 covered with a coat of paraffin 1 cm. thick. First of all it was 

 ascertained that action of light by itself did not excite an electrical 

 current. It then appeared that the deflection of the galvanometer 

 was increased just as much irrespective of the direction of the 

 current. So the decrease» of resistance is independent of the direction 

 of the current. By interposition of coloured glass plates I got a 

 rough estimation of the relative influence of the different colours 

 of the spectrum. Thus I found : 



White light, placed at 16cms'. distance, makes the conductivity rise to 200% of its original value 



■"■ e( l n 11 11 n n m 11 11 ii n i' '"■* ,o ii ii ii v 



Urange „ „ „ „ „ „ „ „ „ „ „ 153% „ „ ,, „ 



Lrreen „ „ ,, „ „ „ „ .. „ „ „ 116% „ „ „ „ 



-E>' ue ii •> m » ii ii ii ii ii ii ii 176% „ „ „ „ 



l ) Not quite the original value. The substance shows hysteresis to a certain 

 amount, which, however, is smaller than for selenium. Already 20 a 40 

 minutes after the source of light had been removed, the original deflection was 

 sometimes found back. The mineral seems to be quite free from any admixture 

 of selenium, as a qualitative investigation taught me. Remarkable in a high degree 

 is the fact, that on melting the natural mineral, it obtains, when solidified as a 

 conglomerate of little crystals, a specific resistance, which is many thousand 

 times less than before, while at the same time it has lost its sensibility to light- 

 radiation quite. On heating the antimonite however, without melting, it conserves 

 this property. Analysis has taught me, that there are present the elements : Sb, S, 

 Ga, Ba, Sr, Si and, as Prof. Kley found, traces of Zn and Co ; also Si0. r crystals 

 are included. (Added in the English translation). 



