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210 Prof. Minchin's Experiments in Photoelectricity. 



through which a current passes ; and to establish this fact 

 more fully the following experiment was made : — 



On a glass plate, ABCD, were cemented, close together 

 but not in contact, several strips of silver foil, a, b, c, d, . . ., 

 the whole plate being uniformly 

 coated with a film of Liverpool emul- 

 sion ; two or more of the silver strips, 

 a, c, were put into the circuit of a 

 bichromate cell, the other strips, b, d, 

 being left out of the circuit. This 

 glass plate with its strips was half 

 immersed in a vessel of water in pre- 

 sence of another silver plate, and the 

 current was passed for a few seconds. 

 On removing the sensitized plate 

 from the vessel and applying the 



developer, the blackening took place only on those strips 

 which were metallically thrown into the circuit, and only on 

 the immersed portions of those strips. 



I made use of this principle in an attempt to transmit an 

 image of a simple figure to a distance ; but the arrangements 

 were so difficult that the success attained was small, and I 

 must leave the matter for renewed trial. 



Eosine. — Comparatively strong currents are obtained by 

 coating a silver plate with an emulsion of eosine and gelatine, 

 and the currents are strengthened by allowing the film to 

 set thoroughly on the plate. But such a plate has the draw- 

 back that the eosine readily leaves the film and comes into 

 the liquid. This passage of the eosine may be delayed by 

 pouring a layer of collodion over the dry gelatine film. By 

 the action of light, this plate is rendered negative to the un- 

 exposed plate. 



When daylight was allowed to fall on this plate, any 

 variation of the light caused by a passing cloud, or the inter- 

 position and withdrawal of the hand in front of the cell, was 

 at once accompanied by a variation of the current strength ; 

 and the same thing is true for all the cells previously de- 

 scribed ; but no variations of sufficient rapidity are produced 

 to affect a telephone, although the make and break of the 

 current itself is, of course, amply sufficient to do so. 



The photographic action on a bromide-of-silver plate placed 

 in a cell in a dark room and connected with one of the poles 

 of an eosine cell was effected by the current generated by 

 daylight in the latter without any preliminary exposure of 

 the bromide plate to gaslight. 



A very curious case of inversion of the current produced by 



