602 PHILOSOPHICAL TRANSACTIONS. [aNNO 1779- 



to heat rooms as the Germans do. My paste-board discs kept very good during 

 all the time I left them in a room constantly warmed, which was about 1 months; 

 but when they were placed in a cold room, they soon lost their power, having 

 probably attracted moisture from the air. I cannot be sure that the varnish I 

 got made for the purpose, was of the best kind : I have reason to suspect the 

 contrary, and therefore I should think that much better might be obtained in 

 London. Such paste-boards might be possibly preserved from attracting mois- 

 ture, by keeping them shut up in a box made on purpose, lined within with tin- 

 foil. The moisture might also be expelled again by placing them a good while 

 in a heated room, or on a baker's oven. 



It seems besides not improbable, that a kind of paste-board might be made by 

 sticking together the lamina of paper, first thoroughly dried, with a good oil 

 varnish, instead of common paste, as this last never can be deprived of its 

 watery particles without losing its cohesive quality. A good kind of paste-board 

 might likewise be contrived by sticking together silk cloth instead of paper. I 

 contrived a plated machine, the disc of which was made of baked wood, and 

 boiled in linseed oil ; but it did not answer near so well as the paste-board discs. 

 I found the paste-hoard discs not much less susceptible of electricity before I had 

 varnished them, than they were afterwards ; but they lost their force again in a 

 few minutes, and did not recover it till they were dried and heated again. It is 

 well known, that writing and brown packing paper, when warmed, may acquire 

 a considerable electrical power by being rubbed with hares' skin, or a piece of 

 wood, or ivory, nay even (as I found by experience) with a metallic body. 



As it seems to be a general law of nature, that all resinous bodies, excited 

 either with a positive or a negative electricity, are more tenacious of keeping it, 

 or seem to part with it, as it were, with more reluctance than glass ; it is ad- 

 viseable, that the conductor of such a paper machine be not furnished with me- 

 tallic points, which being necessarily kept at a distance will not take away all the 

 electricity ; but that some flexible, conducting substance, as silver or brass lace 

 fringes, communicating with the conductor, be in close contact with the excited 

 surface. As woollen cloth or Manchester cotton velvet, and such like substances, 

 excite a good deal of electricity on dried paper and resinous substances, and do 

 not wear out so soon as hares' skin, it might, perhaps, be found better to substi- 

 tute them for hares' skin, I have also excited a very considerable electrical force 

 on strong silk velvet, tied upon the circumference of 2 wooden discs, 2 feet in 

 diameter, and distant about 3 feet from each other, fixed on a wooden axis. The 

 velvet was supported by a strong silk cloth tied under it, in order to give it more 

 strength and steadiness. This machine had the appearance of a drum, and was 

 whirled round, as is usually done with glass cylinders. The rubber was a cushion 

 covered with hares' skin. As silk cloth, and more particularly oiled silk, very 



