KOTICES CONCERNING PHILOSOPHICAL APPARATUS. 217 



of an inch thick. The whole furface was 4S fquare inches, 

 which multiplied by 20, anfwers to 960 fquare inches of glafs 

 in capacity, or almoft feven fquare feet. It is nece(fary that 

 a card fhould be placed between each plate of talc and its 

 neighbour, and hence by an eafy computation, it is found that 

 the talcs and cards (of T % of an inch thick), requifite to an- 

 fwer to 100 feet of glafs would be about 3f inches thick. . 



This instrument for the purpofes of low intenfities would be size of a battery 

 incomparably cheaper and more manageable than glafs. In- equivalent tq 



ill /• • n r i r 7- i i 2 0>°00 fquare 



deed a battery anlwenng to twenty thouland lquare feet would f eet# 

 be very portable, and might be put into a box of one foot 

 fquare and two feet deep. But it mull be remembered that 

 the intenfity cannot be greater than to give an explofive fpark 

 of one thirteenth of an inch, or lefs, and confequently that 

 this apparatus is limited to experiments requiring no greater 

 intenfity. 



The conftruc~tion is that defcribed by Beccaria, in his arti- Beccaria's 

 ficial electricity. Fig. 2. reprefents the arrangement of the atter y* 

 plates of talc with fquare coatings of tinfoil between them. 

 From each coating alternately fucceeds a tail, fo that all the 

 pofitive fides unite above, and all the negative below. » In • • * 



Fig. 1. the wire c. communicates with all the coatings of one 

 kind, and the wire a in like manner unites all the coatings 

 from the oppofite fides j and at b is an infulated fcrew wire 

 forming the electrometer of Lane. The pillar fupporting the 

 fcrew e may either be of glafs or other infulating matter, or 

 elfe a piece of amber, d may be placed between the battery 

 and e. In my apparatus, the talcs were confined between two 

 fquares of glafs, and on the outfide of thefe were two fmaller 

 pieces of wood as in the figure. 



I did not make many experiments with this battery, becaufe 

 the fpontaneous explofions of one plate ufuaily broke all the 

 reft, and it was my intention to have them fomewhat thicker, 

 and to have interpofed cards between plate and plate. But 

 other purfuits have hitherto prevented my refuming this object. 



Complex Ilorfefhoe Magnet. 



Fig. 3. in ihe fame Plate XI. was given me by the late Complex horfe- 

 George Adams of Fleet Street. It was wrapped in a paper on ftoe ma S net » 

 which the workman who made it had written the following 

 Wprds. 



" The 



