VOL. LXIV.] PHILOSOPHICAl, TRANSACTIONS. 363 



rounded off, and made perfectly smooth. I covered the platina with a piece of 



thick plate-glass; and then discharged through it, 3 jars containing 1 6 square 



feet of coated surface: when I obtained many beautiful spherules of the platina. 



Several of them stuck to the wax and glass; and others imperfectly formed, on 



the edges, &c. of the grains; which proved that the fusion had been complete. 



Exper. 8. I made a long cork perfectly dry, and held one end of it very near 



the fire, till it began to burn. At the same time I held a small fine toothed file 



in the clear part of the fire, till that also had become very dry, and rather hot. 



Then, having filed off the end of the cork, I applied it to a pair of neat light 



pith balls; when it attracted them both, and raised them perpendicularly, as high 



as the strings would permit. Having electrified the balls by excited amber, the 



cork would increase their divergence from 1 to near 2 inches? or it would repel 



them at an inch distance, so as to drive them 1-i- inch out of the perpendicular. 



Electrifying the balls by excited glass, these appearances were directly reversed. 



The cork therefore had parted with its electricity to the file, and plainly acted as 



a negative electric. ^j 



Exper. 9. Having neatly rounded off the corners of a piece of thin talc, 



about 3 inches square; I coated both its sides within 4 of an inch of the edges, 



with tin-foil, which I also rounded off at the corners. The talc, thus prepared, 



I observed would readily charge, without wiping, or drying the uncoated part, 



and the force of the shock, in the discharge, was really astonishing. 



Having been shown, by my late truly ingenious friend Mr. Canton, an elec- 

 tric spark, of a very beautiful crimson colour, which always appeared as it was 

 drawn over, or through, a piece of smooth wood, at the top of the conductor- 

 stand, and which was supposed by some gentlemen to be the light of electricity^ 

 very thinly spread on the surface of the wood; I was exceedingly desirous to 

 know from what cause this phenomenon really proceeded; and for that purpose 

 made the following experiment. 



Exper. 10. I fixed between 2 balls, introduced into the circuit of an electric 

 discharge, a piece of smooth wainscot, about 1 inches in diameter, and a quarter 

 of an inch thick; when, on making the discharge of a pretty large jar, I ob- 

 served the wainscot to be nearly covered with the electric light, the outer parts, 

 or edges of the light, were exceedingly thin, but the colour very white, as it was 

 also in several other experiments, made with the same intent. I then procured 

 a circular piece of coloured box, which was glued to the top of the stand to my 

 prime conductor ; when, drawing strong sparks through this wood, of whatever 

 colour it was, I became clearly of opinion, that the colour of the spark varied 

 according to its depth in the wood, viz. if it passed on the surface, it was white, 

 a little below it, yellow, or orange: still lower, scarlet: and deeper in the wood, 

 crimson. 



4c 2 



