. Student's manual of electro-therapeutics, embodying lectures delivered in the course on therapeutics at the Woman's medical college of the New York infirmary. dy we call positive, anddesignate with a +. A body is of low poten-tial when electricity will flow from the earth toit, and this body we call negative, and desig-nate by a ?—. These standards of comparison for potentialand temperature are arbitrary, hence the termspositive and negative (+ and —), hot and cold,are relative terms only. For instance, judgingby our feelings, bodies at Jo° C. and ioo° C. areboth hot, but compared with each
. Student's manual of electro-therapeutics, embodying lectures delivered in the course on therapeutics at the Woman's medical college of the New York infirmary. dy we call positive, anddesignate with a +. A body is of low poten-tial when electricity will flow from the earth toit, and this body we call negative, and desig-nate by a ?—. These standards of comparison for potentialand temperature are arbitrary, hence the termspositive and negative (+ and —), hot and cold,are relative terms only. For instance, judgingby our feelings, bodies at Jo° C. and ioo° C. areboth hot, but compared with each other thebody at ioo° C. is hot, while that at 7o°C. is cold. GALVANISM. 3 In the same way two have poten-tials, one seventy and the other one hundredtimes that of the earth, and hence both be posi-tive, and yet, really, as compared with eachother, the one with the lower potential is nega-tive to the higher, and the one with the higheris positive to the lower. A more apt illustration is that alluded to byDe Watteville, i. e., to compare elements ofdifferent potentials to reservoirs at differentlevels ; for instance, z. and c, fig. If these reservoirs be full of water its tendencyto seek a lower level corresponds to the poten-tial of the elements. If they be connected by apipe we will see that the higher cistern will 4 ELECTRO-THERAPEUTICS. commence to empty itself into the lower. Acurrent is thus established. The force startingthis current is, in one case the force of gravity,and depends on the difference of level of thetwo reservoirs ; in the other case it is the elec-tro-motive force, and depends on the differenceof potential of the two elements. A galvanic cell, in its simplest form, consistsof two dissimilar metals (c. and zn.) immersedin a corrosive liquid. (Fig. 2.) - Fig.
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