and on ike Pyro-Electricity of Glass. 34« Y 



stopped. Having shown this novel experiment to some sci- 

 entific friends, it was suggested that the electricity might be 

 produced by currents of heated air circulating around the 

 glasses. To ascertain this, I blew with a bellows on the glasses 

 without stopping the rotations : these revolutions are explained 

 by the before-mentioned diagram, and arise from attraction 

 and repulsion. To show beyond doubt that the phaenomenon 

 was electric, I removed one of the glasses and brought the arm 

 of the needle so as to touch the other glass ; it was immedi- 

 ately repelled, and both arms stood parallel to a tangent, some- 

 times one arm being somewhat attracted and then repelled. 

 A heated glass tube attracted either arm. When the doors 

 were shut the revolutions decreased ; this did not arise from 

 any draught up the chimney, but from pure air being more fa- 

 vourable than stagnant and warm air, in some measure de- 

 prived of its oxygen. I now dipped my tumblers in water, 

 and on replacing them the velocity was increased to one hun- 

 dred in a minute; filling them with cold or hot water made 

 no difference. Did the evaporation increase the electricity ? 

 I also caused the needle to revolve between two cylinders of 

 china, which I afterwards powerfully excited with a silk hand- 

 kerchief. These experiments, if confirmed, open a new and 

 wide field in the science of electricity, which 1 hope may be 

 cultivated with success. 1 have come to the conclusion, after 

 numerous experiments, that all bodies reflecting radiant heat 

 become electric, even different coloui-ed cloths ; and conse- 

 quently that radiant heat and electricity are mutually convert- 

 ible. When the needle was placed in the focus of the iron- 

 curved side of the grate, it became electric and revolved. I 

 found also that the needle revolved in the focus of a polished 

 mirror, opposite a fire or another mirror, with a heated ball, 

 similar to the late Sir John Leslie's experiment. I am almost 

 sanguine enough to believe that a very delicate needle may 

 be made magnetic by radiant heat, such as that of the sun. 

 I believe Mrs. Somerville advanced the same opinion. 



On returning from the Polytechnic Institution*, highly 

 pleased with Mr. Armstrong's hydro- electric machine, I 

 placed a bright copper kettle, more than half-full of distilled 

 water, on the fire, insulated by four black bottles; when ra- 

 pidly boiling I placed the revolving electrometer near it on the 

 hob, the revolutions immediately began ; after continuing for 

 some time I took off the cover, still the revolutions proceed- 

 ed, but somewhat decreased. Were I to venture an opinion 



* The author begs leave to thank Prof. BachofFner and the gentlemen 

 of that Institution, for their courtesy in permitting hina to experiment with 

 their powerful apparatus. 



