Light Action in Certain Crystals of Metallic Selenium. 505 



just the same as if they had impinged at the same spot. 

 The mean distance between these two illuminated areas was 

 3 mm. 



The Action of Light in a Crystal is transmitted to a Dis- 

 tance. — The above result led directly to a peculiar experiment 

 with the amazing result that light action may be transmitted 

 laterally to a longer distance than 10 mm. in an acicular 

 hexagonal crystal of metallic selenium without any, at present 

 known, apparent mechanism to carry the action. First a 

 crystal of dimensions 10 x *12X'13 mm. was placed with one 

 end between silver electrodes, as shown in fig. 3. The con- 

 ductance in the dark was 110. A beam of light was focussed 



first near the electrodes, and then moved out to the end step 

 by step, and the following readings of the conductance were 

 observed. 



Tajjle IV. 



Location of 

 light. 



Conductance, 

 0. 



Change in 



Conductance, 



AC 



Off crystal. 



110 







Near electrodes. 



144 



34 



On Step 1. 



137 



27 



o 



117 



7 



„ „ 3. 



111 



1 



„ ,- 4. 



124 



14 



., „ 5. 



14G 



36 



„ 6. 



150 



40 



On end of crystal. 



151 



41 



This shows, as did also similar experiments with other 

 crystals, that along the crystals there are light-sensitive parts 

 which control the conductivity mechanism of the selenium. 

 For, strange enough, the greatest effect was produced in the 

 crystal above when the illumination was at the end of the 

 crystal farthest from the electrodes, a distance out of some 

 6 mm. If the current had travelled the entire distance 

 around by way of the illuminated end, it would have gone 



