Ele^iical Appui-atu!.*~Neiv Air-Pump. 44tt 



C F, the paflage which the lightning may take, according to the fecond Cafe of this 

 Experiment, and damage the fame building at F, if the limit of charged air be at A 2 ; or 

 the building near to it, if the limit of charged air be at A 3. 



References to Fig. II. 

 A A, the exterior cylinders. 

 B B, the interior cylinders. 



The interval between tliem is {haded, and contains the air which is charged.' 

 A A, the metallic rod which connefts the exterior cylinders. 

 B B, the metallic rod which connefts the interior cylinders. 

 C, thecondu£lor. 



D and E, the two infulated metallic balls. 



C D, the glafs tube of water which connefts tJie conduflor C with the ball D. 

 E R, a metallic rod, which connects the ball E with the communication B B, between 

 the interior cylinders. 



F, fome inflammable fubftance, as rofin mixed with cotton, placed between the balls D E. 



G, a metallic rod, to reprefent any metallic fubftance belonging to the building, to be 

 placed or removed at pleafure. (It was ufed in the fourth Cafe, but was removed from the 

 apparatus in the fecond Cafe.) 



H H, circular pieces of cork covered with tinfoil, fixed to a metallic rod P H. 



This rod P H is fixed at O, into a glafs pillar of about ten inches in height ; the lower 

 end of the glafs pillar is fixed into the centre of a wheel S, which turns upon a pivot that is 

 fixed into tlie table T. 



The edges of the wheel S being grooved, two cords are .applied to the two grooves. Thefe 

 cords, pafTmg through pulleys in the table and alfo in the ftand of it, are conveyed to the 

 hand of the perfon who is turning the cylinder of the eledrical machine, by which means 

 he can make the body H revolve at pleafure. 



From the rod at O rifes a metallic ftem, with a fwivel upon the top of it. To this fwivel 

 is fixed K L, which connefts it with the exterior cylinder A. 



Over the top of this ilem below the fwivel pafles a cord, fixed at one end to the centre of 

 H, and at the other to the balance weight P, which ferves to keep PH in an horizontal 

 pofition. 



M N, a metallic rod which conneds the exterior cylinders A A with the pofitive con^ 

 iuHor of the eleiSlrical machine. 



The metallic rod M N is about eight feet above the floor of the room, and the moveable 

 rod P H traverfes at about fix feet above the floor. H. H. 



II. 



New ConJiniBkn of the Air-Piimp. By JaMF..^ Sadler, Efq. Chemijl to the Admiralty. 



A HEconftru£lion of the air-pump, with the improvements of Mr. Cuthbertfon and the 

 Rev. J. Prince, have been explained in a former communication *. In order that the cfrcft 

 of tins iiiftrument may be as pcrfed as its theory will allow, it is neceflary that its valves 



' Pliilofophlcal Jouior.1, i. 119. 



Vol. I.— January 1798. -sL flio^U 



