332 Ettflrifal Fly. [Book IV, 



A wire is fometimes fixed to the under part of the 

 infulated coated phial (Fig. 5.) and be is another v/irc 

 fitted to, and at right angles with die former j a brafs 

 fly (Fig. 4.) is placed on the point of this wire j charge 

 the bottle, and all the time the bottle is charging the 

 fly will turn round j when it is charged the needle will 

 flop. If the top of the bottle is touched with the 

 finger, or any other conducting fubftarite, the fly will 

 turn again till the bottle is difcharged. The fly wiil 

 electrify a pair of balls pofitively while the bottle is 

 charging, and negatively, when it is difcharging *. 



When a Leyden phial pofitively charged is infulat- 

 ed, it will give a fpark from its knob to an excited 

 flick of wax, but not a fpark will pafs at that time 

 between it and an excited glafs tube. 



An additional quantity of the fluid may be thrown 

 on one fide of the jar, if by any contrivance an equal 

 quantity may be made to efcape from the other, and 

 not otherwife. 



Electricians, in order to increafe the force of the 

 electric explofion, connect feveral Leyden phials toge- 

 ther in a box j and this collection they call an electri- 

 cal battery. 



In this apparatus the bottom of the box (Plate 

 XXVII. Fig. 2.) is covered with tin-foil, to connect 

 the exterior coatings ; the infide coatings of the jars, 

 are connected by the wires a, b, c> d y e,f, which meet 

 in the large ball A ; C is a hook at the bottom of the 

 box, by which any fubftance may be connected with 

 the outfide coating of the jars ; a ball, B, proceeds 

 from the infide, by which the circuit may be conve- 

 niently completed. Mr. Adams gives the following 

 precautions to thofe who make ufe of an electrical 

 battery f . 



* Mr. Adams's Eflay on Eleft. p. 131. f Ibid. p. 14-;. 



The 



