GALVANISM. 



27 



upright electrical columns be placed side 

 by side, with their poles in opposite di- 

 rections, and connected at their upper 

 ends, while a small bell is attached to 

 the lower end of each ; the whole will 

 act as one column, and each bell will, 

 in consequence of the electrical actions, 

 be alternately struck by a brass ball 

 suspended between them; and thus a 

 continual ringing will be produced as 

 long as the machine remains in action, 

 which is generally for a considerable 

 time. This action is, however, kept up 

 solely by the presence of moisture in the 

 paper, for it does not take place at x all 

 when the paper is perfectly dry; and 

 although the process of oxidation is very 

 slow, the more oxidable metal is in pro- 

 cess of time found to be tarnished. 



(92.) An apparatus somewhat analo- 

 gous to that of De Luc was constructed 

 by Hachette and Desormes with pairs 

 of metallic plates, separated by layers of 

 farinaceous paste, mixed with common 

 salt. To this instrument, although it 

 evidently owed its efficacy to the mois- 

 ture of the paste, they gave the very in- 

 appropriate name of dry pile. It has 

 the same properties as the electric 

 column, except that it is unable to give 

 a shock. A pile having nearly similar 

 powers was also constructed by Profes- 

 sor Zamboni, of Verona, with discs of 

 paper, gilt or silvered on one of their 

 sides, while the other side was covered 

 with a layer of pulverized black oxide of 

 manganese, mixed with honey. Both 

 this and the former instrument retained 

 their power fora great length of time. 



(93.) Piles formed simply of discs of 

 copper and moistened card, placed al- 

 ternately, were found by Ritter to have 

 no power of developing electricity by 

 their own action, but to be capable of 

 receiving a charge by being placed in the 

 circuit of a powerful voltaic battery, 

 and of thus acquiring, though in an 

 inferior degree, all the properties of the 

 battery itself from which it derived its 

 activity. The properties of these se- 

 condary piles, as they have been called, 

 are obviously the effect of a series of 

 electrical inductions, extending from end 

 to end ; and the apparatus is found to 

 retain its charge for a very considerable 

 time, provided it be kept insulated, and 

 the communications between the two 

 poles are not renewed too frequently. 



(94.) Having thus traced the various 

 ways m which galvanic power may be 

 excited, we have next to examine the 

 influence of different circumstances, by 



which its quantity, intensity, and mode 

 of action are regulated. We have al- 

 ready seen that the intensity of the 

 electricity developed by a single galvanic 

 circle, bears no relation to the extent of 

 surface of the elements which compose 

 that circle. It follows, therefore, that 

 however much we may increase the 

 quantity of electricity by employing very 

 large plates, as in the calorimotor, we 

 cannot obtain from such an instrument 

 any of those effects which require for 

 their production a certain intensity, as 

 well as quantity of electricity. In order 

 to obtain these latter effects, we must 

 employ the compound battery, consist- 

 ing of a considerable number of alter- 

 nations of the same elements. The 

 former of these instruments, accord- 

 ingly, will be capable of producing such 

 effects as depend upon mere quantity,"" 

 without regard to intensity ; such as 

 the evolution of heat, the ignition and 

 deflagration of the metals, and electro- 

 magnetic phenomena. The compound 

 apparatus, on the other hand, will afford 

 the more ordinary electric appearances, 

 (such as the spark, and the phenomena 

 of attraction and repulsion,) will affect 

 the electrometer, or condenser, and will 

 communicate a charge to a Leyden jar; 

 for in all such operations, intensity of 

 electricity is the most essential requisite, 

 and the power of the battery to produce 

 them is found to be augmented by 

 every increase in the number of the 

 alternations. But there is also a third 

 class of effects, more peculiarly apper- 

 taining to galvanism, which take place 

 by the transmission of the electric cur- 

 rent through bodies of inferior conduct- 

 ing power ; such as liquids of various 

 kinds, and living organized structures, 

 both animal and vegetable : producing 

 in the former chemical decomposition, 

 and in the latter various physiological 

 effects, such as nervous excitation, 

 muscular contraction, and affections of 

 secretion. For the production of these 

 effects it is necessary, not only that the 

 electricity be sufficiently powerful, 

 both in respect to intensity and to 

 quantity, but also that it should flow in 

 a continuous current. It is from the 

 difficulty of supplying this latter re- 

 quisite, that the electricity derived from 

 the common electrical machine, is, 

 under ordinary circumstances, incapable 

 of decomposing water in the way that 

 is so readily accomplished by voltaic 

 electricity. It is from deficiency of 

 intensity, on the other hand, that we are 



