234 "Journal of Experiments, 1772 



sep. full i diam. did not close soon. 



do. 



do. 



do. 



do. 



seemed more, but not quite certain. 



seemed pretty certainly less. 



sep. about I diam. closed faster. 



do. 



do. 



do. 



sep. but certainly less. 



sep. about i diameter*. 



484] Two of the old ground glass plates H, I, K, L of Nuremberg glass f, 

 were coated with oblong squares to serve for trial plates to the plates I, K, L, M 

 of Nairne, but the observations were found to be so irregular that nothing could 

 be made of them, owing, as was supposed, to the spreading of the electricity 

 on the surface of the glass. 



To prevent this, all the four plates H, I, K and L were coated with oblong 

 squares, and cased in cement composed of 2 parts rosin, i of bees' wax, and 

 3 of brick dustf. 



In making it the bees' wax was first melted and imperfectly dephlegmaied, 

 the rosin was then added and melted with as little heat as possible, and then 

 the brick dust, previously heated so as to be very dry, was added. By this 

 means the cement is more safe and sticky than if more heat is used in making it. 

 In some of the mixtures also a small part of the rosin, never exceeding J th of 

 the whole, was exchanged for as much pitch, which was added after the rest 

 was melted and mixed. 



The plates E, F, G, and I, K, L of Nairne were cased in the same cement, 

 about -165 thick. 



A plate of the same cement was also cast by pouring it out on a tin plate. 

 This was coated with circles about 2-2 in diameter. 



485] The spreading of the electricity on the surface of the trial plates 

 seemed not to be prevented by casing them in cement, for putting the plate L 

 of Nairne on the positive side, and the trial plate H on the negative, then if the 

 apparatus was let down and drawn up again immediately J, the pith balls sepa- 

 rated about half an inch negatively, but if the apparatus was suffered to rest 

 at the bottom about half a minute, and then drawn up immediately, they 

 separated considerably more than i inch, and if it was suffered to rest at the 



[See Art. 655.] 



f [See Art. 303.] 



J [See Art. 302.] 



