10 



GALVANISM. 



fects, the wire proceeding from one ex- 

 tremity of the battery should be con- 

 nected with the foot of the electrometer ; 

 while the wire proceeding from the op- 

 posite extremity is made to touch the 

 cap. It was by means of the revolving 

 doubler (see Electricity, 195.) that 

 the electrical states of the two ends of 

 the voltaic pile were first ascertained by 

 Messrs. Nicholson and Carlisle.* 



(23.) Since the ends of the two wires, 

 which proceed from the two poles [of 

 the voltaic battery, are in opposite states 

 of electricity, we might naturally expect 

 that they would attract one another. 

 Such an attraction actually does take 

 place, as Biot found by experiment ;f 

 but it does not become sensible, unless 

 a battery composed of a great number 

 of plates is employed, 



(24.) The general conclusion dedti- 

 cible from the facts that have now been 

 stated, is that the intensity of the elec- 

 tricity developed by galvanic combina- 

 tions is increased, according as the 

 number of alternations in the elements 

 which compose them is greater, and 

 that it bears no proportion to the mag- 

 nitude of their surfaces. 



(25.) If the voltaic battery be of suf- 

 ficient size, its electricity may be trans- 

 ferred to a common electrical battery, 

 which will then become charged to the 

 same degree of intensity. Nothing more 

 is necessary for this purpose than to 

 connect the outer and inner coatings of 

 the electrical battery, respectively, with 

 the two poles of the voltaic battery ; 

 when the charge will be instantly com- 

 municated to the former. If on re- 

 moving it from the voltaic battery this 

 electricity be discharged, and the same 

 communications be renewed, a similar 

 charge will again be received ; and the 

 same process may be repeated an in- 

 definite number of times. If, instead 

 of removing the electrical battery, we 

 allow it to remain connected with the 

 voltaic battery, a rapid succession of 

 sparks may be obtained from it by con- 

 necting a wire with the outer coating, 

 and repeatedly striking the knob of the 

 phial with the other end of the wire. If 

 the series of plates in the voltaic battery 

 consist of three or four hundred alter- 

 nations, these rapid explosions are so 

 powerful as to ignite the end of the wire, 

 if it be of iron, and to cause it to throw 

 off an abundance of sparks, consisting 



* Nicholson's Journal, 4(o. iv. 174. 

 t Biot, Traite de Physique, ii. 511. 



of small particles of iron in a state of 

 intense combustion. With a series of 

 one thousand, each discharge is at- 

 tended with a sharp sound, and will 

 burn thin metallic leaves. This is the 

 more remarkable as the same voltaic 

 battery may not have sufficient power 

 to produce these effects by itself, or un- 

 connected with an electrical battery. 

 The shortest possible contact with the 

 voltaic battery is sufficient for giving 

 the whole of the charge which it is ca- 

 pable of communicating. This was ap- 

 parent in some experiments made by 

 Van Marum and Pfaff with a battery 

 having 137 square feet of coated sur- 

 face, and which was charged to the 

 same degree of intensity as the pile with 

 which it was made to communicate, by 

 a contact which did not last for the 

 twentieth part of a second.* 



$ 2. Luminous effects of Galvanism. 



(26.) It is only when the electricity of 

 a voltaic battery possesses a sufficient 

 intensity, that it becomes capable of 

 passing through air. With the calo- 

 rimotor the intensity is too feeble to 

 enable it to traverse the smallest per- 

 ceptible interval between metallic con- 

 ductors, so that they must be brought 

 into actual, or at least apparent, con- 

 tact, before any sensible effect is pro- 

 duced. In a pile or trough battery, on 

 the other hand, composed of a consider- 

 able number of alternations of plates, 

 on bringing together the wires from the 

 opposite poles, the transfer of electricity 

 begins while they are yet at a sensible 

 distance from one another : and as in 

 the case of ordinary electricity, this tran- 

 sit through the air is accompanied by 

 vivid light. The sparks occur every 

 time the contact between the wires is 

 broken, as well as when it is renewed. 

 This phenomenon, which does not take 

 place with the electricity furnished by 

 the ordinary means, is characteristic of 

 voltaic electricity, and is a consequence 

 of its continuous supply. The stream 

 continues to flow, notwithstanding the 

 interruption to the line of circuit, and 

 as long as the conductors remain within 

 the striking distance ; and although this 

 happens only for an instant, there is 

 still sufficient time for the appearance 

 of a spark. 



(27.) The most splendid exhibition of 

 electric light is that obtained by placing 

 pieces of charcoal, shaped like a pencil, 



Annales de C/iimie, xl. 289. 



