564 rHILOSOVHICAL TRANSACTIONS. [aNNO 1774. 



It having been mentioned by some gentlemen, as their opinion, that the 

 matter of light, and the electric matter, were the same thing; I made the fol- 

 lowing experiment, in order to determine whether there was any foundation for 

 such an opinion. 



Exper. 11. I insulated the rubber of my machine, and placed it in such a 

 situation, that the rays of the sun, passing through the open window of my 

 room, might fall immediately on it; but this I observed produced no electricity. 

 I then collected the rays into a focus, by means of a good convex glass, and 

 threw them on the back of the rubber, till it was burned quite black; but this 

 method was attended with no better success. I then mounted one of Mr. Can- 

 ton's electrometers, furnished with very light balls, on a stand of sealing-wax; 

 and having electrified them negatively, by excited amber, so as to diverge a full 

 inch, I again collected the rays of the sun by the convex glass, and held it at such 

 a distance as to bring the focus exactly on the end of the box, which was burnt 

 very black, and the glue in the joints melted ; but the balls were not in the least 

 affected. 



Exper. 12. Hold a piece of amber near the flame of a candle, till it becomes 

 hot: then apply it to a suspended thread, and it will not attract it, neither will 

 it become electrical in cooling; but press it ever so lightly on your hand, in 

 order to try its heat, though without the least friction, and, if it be not too hot, 

 it will be electrical, and attract it violently. Heat it again at the candle, and its 

 electricity shall be taken quite away. Press it again gently on your finger, or 

 hand, and the power will be restored. Apply it again to the candle, it is lost. 

 And thus alternately. Other electrics may probably act in the same manner; as 

 the flame of a candle, or hot air, will conduct away the electricity of glass, al- 

 most instantaneously. 



Exper. 13. Showing Mr. Nairne the above-mentioned experiments: when the 

 amber had been well heated, and being presented to a suspended thread, having 

 shown no sign at all of electricity; I held it, between my thumb and fore-finger, 

 very near the table, but not so as to touch it, that we might entirely avoid fric- 

 tion. He then blew against it 30 blasts, with a pair of kitchen bellows; when 

 presenting it to the thread it attracted it, at the distance of J- of an inch. He 

 then blew against it 30 blasts more, as above described; when applying it again 

 to the thread, we saw it attracted at half an inch distance; and on drawing back 

 the amber, it drew the thread after it 6 or 8 inches. We repeated the experi- 

 ment 3 times with the like success; and are satisfied, that the amber was made 

 electrical by the friction of the particles of air against its surface : and not in the 

 least by heating only. We afterwards excited the amber, when it must have 

 been perfectly cold, but dry, by only blowing against it as before. The same 

 process succeeds with glass. 



