18 



0ALVANISM. 



a finger of each hand into two separate 

 vessels filled with water, into which the 

 extremities of the two wires from the 

 battery have been immersed. The shock 

 received from the voltaic pile is similar 

 to that resulting from a large electrical 

 batfery very weakly charged : and its 

 intensity is greater in proportion to the 

 number of series of elements composing 

 the pile. Twenty pair of plates are ge- 

 nerally sufficient to give a shock, which 

 is sometimes felt in the arms : with a 

 hundred pair it extends to the shoul- 

 ders. 



(57.) Independently of the shock felt 

 on the first impression of voltaic elec- 

 tricity communicated from the battery, 

 the continued flow of the current 

 through the body, as long as it forms 

 part of the circuit, is generally accom- 

 panied by a continued aching pain. If 

 it pass through any external part de- 

 prived of cuticle, it produces a severe 

 smarting or burning sensation, which, 

 if the exposed surface be large, continues 

 to increase till it is scarcely support- 

 able. This painful feeling is experienced 

 if the slightest cut, burn, or excoriation of 

 any kind, happen to be in the path of 

 the electrical current : and it will be ex- 

 cited in these parts, even by a single 

 pair of plates, forming a galvanic com- 

 bination. It has been remarked by 

 Volta that the pain is of a sharper kind 

 on those sensible parts of the body, in- 

 cluded in the circuit, which are on the 

 negative side of the pile ; that is, where 

 the electricity flows out from the body, 

 than where it enters : a fact which has 

 also been noticed with regard to the 

 pungency of the common electrical 

 spark.* 



(58.) The impression made by voltaic 

 electricity on some of the nerves of the 

 face, when they form part of the circuit, 

 is accompanied by the sensation of a 

 vivid flash of light. The simple appli- 

 cation of a piece of zinc and one of silver 

 to the tongue or lips, frequently gives 

 rise, at the moment of the contact 01 the 

 metals, to this perception of a luminous 

 flash : but the most certain way of ob- 

 taining this result is to press a piece of 

 silver as high as possible between the 

 upper lip and the gums, or to insert a 

 silver probe into the nostrils ; while, at 

 the same time, a piece of zinc is laid 

 "upon the tongue ; and then to bring the 

 two metals into contact. Another mode 

 is to introduce some tinfoil within the 



Nicholson's Journal, 4to. iv. 180. 



eyelid, so as to cover part of the globe 

 of the eye, and place a silver spoon in 

 the mouth, which must then be made to 

 communicate with the tinfoil by a wire 

 of sufficient length ; or conversely, the 

 tinfoil may be placed upon the tongue, 

 and the rounded end of a silver probe 

 applied to the inner corner of the eye ; 

 and the contact established as before. 

 The flash which results from the action 

 of a pile, applied in this way, is very 

 powerful ; and if the plates were nume- 

 rous, the experiment might occasion 

 permanent injury to the sight. This 

 phenomenon is evidently produced by an 

 impression communicated to the retina, 

 or optic nerve, and is analogous to the 

 effect of a blow on the eye, which is 

 well known to occasion the sensation of 

 a -bright luminous coruscation, totally 

 independent of the actual presence of 

 light. In like manner the flash from 

 galvanism is felt whether the eyes be 

 open or closed, or whether the experi- 

 ment be made in day-light or in the 

 dark. If the pupil of the eye be watched 

 by another person when this effect is 

 produced, it will be seen to contract at 

 the moment when the metals are brought 

 into contact. A flash is also perceived 

 at the moment the metals are separated 

 from each other. 



(59.) The peculiar taste which is per- 

 ceived when different metals are applied 

 to different parts of the tongue, and 

 made to touch each other, has already 

 been noticed. It is essential to the 

 success of the experiment, that the sur- 

 face of the tongue should be moist; 

 for when the tongue is previously wiped 

 very dry, the effect is considerably di- 

 minished, and it is not at all perceptible, 

 if the surface is absolutely dry. The 

 quality of the metal laid upon the tongue 

 influences the kind of taste which is 

 communicated ; the more oxidable metal 

 giving rise to an acid, and the less oxi- 

 dable metal to an austere or alkaline 

 taste. Similar differences have been 

 observed by Berzelius, with regard to 

 the sensations excited in the tongue by 

 common electricity, directed in a stream 

 upon that organ, from a pointed con- 

 ductor; the taste of positive electricity 

 being acid, and that of negative electri- 

 city caustic and alkaline. This circum- 

 stance would tend to prove that the 

 taste perceived in the galvanic experi- 

 ment is owing to the actual presence of 

 acids and alkalies, derived from the 

 chemical decomposition of the salts 

 contained in the saliva, by the galvanic 



