90 



PEOFESSOE TYNDALL ON THE INFLrENCE OE COLOUE 



I subsequently endeavoured to get rid of the sulphur cement and to make the powders 

 adhere by wetting them with pure bisulphide of carbon, applying them to the cubes 

 while wet. Some of the powders clung, others did not. My ingenious friend Mr. 

 DUPPA suggested to me that the powders might be held on by electrifying the cubes. 

 I tried this plan, and found it simple and practicable. It was, however, aided by a 

 circumstance which we did not anticipate. The cube being placed upon an insulating 

 stand, the powder was shaken over it, and electrified by a few turns of a machine. It 

 was found that the cube might then be discharged and set upright, the powders clinging 

 to it in this position. The results obtained -with, this arrangement are recorded in the 

 following Table : — 



Table II. — Radiation from Powders held by Electricity. 

 Substance. Eadiation. 



Rock-salt 24-5 



Chloride of Silver (white) . . 25-0 



Milk of Sulphur 25-8 



Biniodide of Mercury . . . . 26*0 



