55* 



ANALYSIS OF THE GALVANIC FILH. 



divergence in the electroscope we use*. Such therefore are 

 the indications of the electroscopes at the extremities of the 

 pile: they express certain degrees of density of the electric 

 Jfuid on them, which are the same whatever be the area of 

 the plates; these degrees depending only on the number of 

 the groups, because each group contributes to increase the 

 density of the fluid on one of the extremities by lessening 

 it on the other. Thus it is that the divergence, both in 

 plus and minus, of the electroscopes, at the extremities 

 of the pile, is proportional only to the number of groups', 

 in the same manner that the height at which water stands 



Reasons for * I shall take this opportunity of explaining why I use the word 



saying elec- electroscope, and not that of electrometer j it is because there is no in- 

 txotkCope. struraent entitled to/ the latter denomination, at least admitted among 



experimental philosophers. Indeed, of our instruments serving to 

 measure the degrees of intensity of physical causes, I know none 

 absolute, except hygrometer?, such as have l>een constructed by Mr. de 

 Saussure and myself; for though these instruments are made of diffe- 

 reut substances, and differ is some other respects, we have obtained 

 m both an absolute zero, and absolute maxima in determined cases, 

 Hygroscopes a* well as determined degrees of intensity, of their object, namely mois- 

 a»d hygrome- ture : all the other instruments inteuded for the same purpose, to my 

 tCiS * knowledge, are only hygroscopes, indicating variations in moisture, with- 



out determined points, or degrees common to them. Thus no kind of 

 physical instrument has yet obtained the conditions of an absolute mea- 

 sure, but the above hygrometers, so little thought of by experimental 

 philosophers, though very important in meteorology. The thermometer 

 has obtained two Jixcd degrees of heat, and determined divisions of the 

 interval between them, by which means experimental philosophers 

 understand one auother when they indicate certain degrees of heat. 

 I have also constructed an eteetrotueter, which possesses the same con- 

 ditions with respect to degrees of electrification, which is described in 

 my work, Jde'es sur la Meteorologies but not having been attended to by 

 experimental philosophers, I have not been induced to follow the ex- 

 tension of this measure down to the minute degrees of intensity indi- 

 cated by the gold leaf electroscope, as I could not expect that it should 

 be more noticed: therefore admirable as is this instrument for its sensi- 

 bility, it affords us no comparable measure. In this imperfect state, how- 

 ever, there is, in every electroscope, a property whieh belongs to no other 

 physical measure, namely, a natural and absolute staudard of plus and minus, 

 which inconstant, as to its general determination, and is the actual elee- 

 r trie state of the ambient air, or the ground ', though variable as to the 



absolute quantity, as are these electric states ; which difference wiH 

 be one of the objects of this paper. 



in 



