22b Prof. Minchin's Experiments in Photoelectricity. 



If, then, I am right in supposing that the development of 

 electrical charges on these sensitive plates is in some way 

 connected with molecular disturbances produced by electro- 

 magnetic induction or mechanical vibration, it must be 

 admitted that the result is possibly a very important one, 

 and that it may play a large part in the economy of nature. 

 Thus, the mode in which solar energy is taken up in the cells 

 of plants may be largely dependent on such disturbances in 

 the atmosphere or in the earth. And in this connexion a 

 somewhat wild conjecture may be pardoned. 



The micro radiometer of Prof. Boys works wonders in the 

 measurement of very minute changes of temperature. If, 

 then, we imagine a beam of light to be incident on the 

 sensitized plate of an impulsion-cell from which it is, in part, 

 reflected to a microradiometer, when the cell is in its insensi- 

 tive state the incident energy is not taken up electrically and 

 statically, and a greater portion of it would be sent to the 

 radiometer than would be sent if the cell were in the sensitive 

 state, so that a mechanical tap or an electromagnetic impulse, 

 in altering the cell from electrical insensitiveness to sensitive- 

 ness, should produce an effect on the radiometer. 



Connexion with the Daniell Cell. — It has been already 

 stated that the residual effect when light is withdrawn from 

 the cell is got rid of by connecting the cell with a Daniell 

 cell in such a way that the deflexion caused by the latter is 

 opposed to that produced by light — L e., the sensitive plate, 

 P (fig. 4), is connected with the copper pole of the Daniell. 



Kff. 4. 



A very curious result of this arrangement deserves to be 

 mentioned, inasmuch as it may possibly afford a clue to the 

 nature of the action of light on the sensitive plate. Between 

 the Zn pole of the Daniell and the plate Q interpose a very 



