Ehge of' Alexander Volta. 11 



observation, and the minute examination of the different circum- 

 stances under which the electrical fluid is developed, which thus 

 pervades all the regions of the air. 



When a branch of science is in its infancy, observers are 

 chiefly occupied in discovering new phenomena, reserving the 

 estimate of their importance to another period. In electricity, 

 many individuals had obtained a well merited reputation ; the 

 Leyden phial adorned all the cabinets of Europe ; but no 

 one had hitherto thought of a true electrometer. The first in- 

 strument of this kind is not of earlier date than 1749 : it was 

 made by two members of this Academy, Darcy and Le Roy ; but 

 its want of mobility under small charges, prevented its adoption. 



The electrometer proposed by Nollet (1752) appeared at first 

 to be more simple and convenient, while it was of infinitely 

 greater sensibility. It was composed of two wires, which, ha- 

 ving been electrified, could not fail to open, by an effect of re- 

 pulsion, like the two arms of a compass. The measure sought 

 was thus reduced to the observation of an angle. 



Cavallo realized what Nollet had merely indicated (1780). 

 His threads were of metal, and supported at their extremities 

 small balls made of the pith of the alder-tree. 



Volta at last laid aside the pith, and substituted dry straws 

 for the metallic threads. This change would appear unimport- 

 ant, were it not mentioned that the new electrometer possessed 

 the valuable and unexpected property, of producing between 0'' 

 and 30° angular dispositions of the two straws exactly propor- 

 tionate to the electrical charges. 



The letter to Lichtenberg, of the date 1786, in which Volta 

 established by numerous experiments the properties of straw 

 electrometers, contains many interesting views on the means of 

 rendering these instruments comparable, on the measure of the 

 strongest charges, and on certain combinations of the electrometer 

 and condensator, of which it is surprising that no notice is taken 

 in any of the more recent works. This letter cannot be too much 

 recommended to young natural philosophers. It will initiate 

 them in the difficult art of experimenting ; it will teach them to 

 distrust first appearances, and to vary incessantly the form of 

 trial ; and if a warm imagination induce them to abandon the 

 slow but certain path of observation, for the allurements of spe- 



