104 PHILOSOPHICAL TRANSACTIONS. [JANNO 1797. 



Having re-appeared in the following April, 1796, it was on the 7th of May again 

 of the 9.10th magnitude, and increasing nearly in a similar manner as on the 20th 

 of June the preceding year; which completes all its changes, and gives a period of 

 10-1- months. 



Very remarkable and perplexing it was, that just after I had made out the periods 

 of these 2 variable stars, their changes should appear different from those before ob- 

 served ; the particulars concerning that in Sobieski's Shield have been noticed : 

 as for this in the Northern Crown, it shows at present (being the computed time of 

 its full brightness), great unsteadiness, more so I think than any of the variables 

 whose periods have been settled with certainty ; for having increased as before, 

 with tolerable regularity, till it attained the 7 -8th magnitude, it then kept wavering 

 between those magnitudes, and is still so at the present time (August) that I am 

 closing my account of it. 



VII. Experiments and Observations, made with the View of ascertaining the 

 Nature of the Gaz produced by passing Electric Discharges through Water, 

 By George Pearson, M. D. t F. R. S. p. 142. 



§ 1. In the Journal de Physique for Nov., 17 89, were published the very curious 

 and interesting experiments of Messrs. Paets van Troostwyk and Deiman, which 

 were made with the assistance of Mr. Cuthbertson, on the apparent decomposi- 

 tion of water by electric discharges. The apparatus employed was a tube 12 inches 

 in length, and its bore -f- of an inch in diameter, English measure; which was 

 hermetically sealed at one end, but before it was sealed, 1-l inch of gold or platina 

 wire was introduced within the tube, and fixed into the closed end by melting the 

 glass around the extremity of the wire. Another wire of platina, or of gold with 

 platina wire at its extremity, immersed in quicksilver, was introduced at the open 

 end of the tube, which extended to within \ of an inch of the upper wire, which, 

 as was just said, was fixed into the sealed extremity. 



The tube was filled with distilled water, which had been freed from air by means 

 of Cuthbertson's last improved air-pump, of the greatest rarefying power. As the 

 open end of the tube was immersed in quicksilver, a little common air was let up 

 into the convex part of the curved end of the tube, with the view of preventing 

 fracture from the electrical discharge. The wire which passed through the sealed 

 extremity was set in contact with a brass insulated ball; and this insulated ball was 

 placed at a little distance from the prime conductor of the electrical machine. The 

 wire of the lower or open extremity, immersed in quicksilver, communicated by a 

 wire or chain with the exterior coated surface of a Ley den jar, which contained 

 about a square foot of coating; and the ball of the jar was in contact with the 

 prime conductor. 



The electrical machine consisted of 2 plates of 31 inches in diameter, and was 

 similar to that of Teyler. It had the power of causing the jar to discharge itself 

 2b times in Lb revolutions. When the brass ball and that of the prime conductor 



