ELECTRICITY 



conducting bodies would appear to have 

 a material influence in determining the 

 striking distance. It was remarked by 

 Dr. Priestley, that the explosion from a 

 large battery extends to a greater dis- 

 tance over the surface of water than in 

 air alone. 



(147.) An effect which seems to de- 

 pond upon this tendency in the fluid to 

 divergence in consequence of obstruc- 

 tion, all hough it has by some been re- 

 ferred to a different principle, is that 

 which has been termed the lateral ex- 

 plosion. When a large jar or battery 

 is discharged '"by a metallic wire which 

 is held in the hand without the protec- 

 tion of any glass or other insulating 

 handle, it often happens that a slight 

 shock is felt in the hand that grasps the 

 wire, especially if the charge of elec- 

 tricity be very considerable. This ap- 

 parent divergence or overflow of electric 

 fluid, when rushing in large quantities 

 through a narrow space barely sufficient 

 to contain it, may also be rendered 

 visible in other ways. If one end of a 

 chain be connected with the outer coat- 

 ing of a charged jar, while the remainder 

 of the chain is lying loosely upon a 

 table, on discharging the jar in a dark- 

 ened room, by a discharging rod, in 

 the usual way* it will be found that the 

 chain, although it makes no part of the 

 circuit, is rendered luminous by the 

 passage of sparks from one link to an- 

 other. The following experiment, made 

 by Dr. Priestley, may also be regarded 

 as a case of lateral explosion. Let a 

 thick metallic rod R, ^. 37, be sup- 

 Fig. 37. 



ported on an insulating stand, and 

 placed with one of its ends in contact 

 with the outer coating of a Ley den jar ; 

 and at a distance of half an inch from 

 its other extremity place a long con- 

 ducting body B, of at least six or seven 

 feet in length, and only a few inches in 

 breadth. Let a chain C, be now placed 

 upon the table, so that one of its ends 

 may be about an inch and a half dis- 



tant from the outer coating of the jar, 

 and apply one end of the discharging 

 rod D, to the other extremity of the 

 chain. As soon as the other ball of the 

 discharging rod is made to touch the 

 knob of the jar, so as to effect a dis- 

 charge, a brilliant spark is seen to ex- 

 tend between the insulated rod R, and 

 the adjacent conductors. This lateral 

 spark has the same length and brilliancy 

 whether it be received on flat or smooth 

 surfaces, or on sharp points. 



It is stated by Dr. Priestley, that 

 the effect we have been describing takes 

 place without any apparent change in 

 the electrical state of the conductor B ; 

 and hence Cavallo conceived that the 

 lateral spark was sent out from the jar, 

 and returned to it almost at the same 

 instant, allowing of no perceptible time 

 for an electrometer to be affected. Dr. 

 Robison, however, always observed, 

 on repeating the experiment, that a 

 very delicate electrometer was affected 

 under these circumstances : and the 

 same observation is confirmed by Biot. 

 The phenomena of the lateral ex- 

 plosion have been attempted to be 

 explained by the electricity exerting, 

 during its passage, an inductive in- 

 fluence, of which the effects may be 

 expected to cease the moment the cause 

 is removed. But this explanation ap- 

 pears to* be less satisfactory than the 

 one which attributes the phenomena to 

 an expansive propulsion, followed by 

 an immediate recession of electric fluid, 

 produced by obstructions to its free 

 passage in the circuit of conductors. 



CHAPTER XL 

 Effects of Electricity upon Bodies. 



(148.) HAVING considered the cir- 

 cumstances attending the motion of 

 electricity with reference chiefly to the 

 fluid itself, we next proceed to give an 

 account of the effects which it produces 

 upon bodies by its passage through 

 them. 



(149.) Independently of electrical at- 

 traction and repulsion, it does not appear 

 that the simple accumulation of electricity 

 in any quantity in bodies, as long as it 

 remains quiescent, produces the least 

 sensible change in their properties. A 

 person standing upon an insulating stool 

 may be charged with any quantity of 

 electricity from a machine, without being 

 perceptibly affected, until the equilibrium 

 of the fluid is disturbed, by drawing 

 sparks from his body, or from the prime 



