{ 36 o ] 



giving it a quantity of the contrary electricity. All 

 thefe purpofes are anfwered, in the mod complete 

 manner, by an electrometer of this gentleman's con- 

 trivance, a drawing of which I fend you along with* 

 the following defcription. 



The whole inftrument is made of ivory or wood, 

 [Tab. XL] (a) is an exceeding light rod> with a cork 

 'ball at the extremity, made to turn upon the center 

 •of a femicifcle (b)> and fo as always to keep pretty 

 -near the limb of ir, which is graduated: fc) is the 

 'item that fupports it, and may either be fixed to the 

 prime conductor, or be let into the brafs knob of a 

 jar or battery, or fet in a ftand, to fupport itfelf. 



The moment that this little apparatus is electrified, 

 the rod (a J is repelled by the item fc), and confe- 

 •quently begins to move along the graduated edge 

 of the femicircle .(b) ; fo as to mark with the ut- 

 moft exactnefs, the degree in which the prime con- 

 ductor, &c. is electrified, or the height to which the 

 charge of any jar or battery is advanced j and as the 

 materials of which this little inftrument is made are 

 very imperfect conductors, it will continue in contact 

 with any electrified body, or charged jar, without 

 •didipating any of the electricity. 



If it mould be found, by trial in the dark, that 

 any part of this inftrument contributes to the dillipa- 

 tion of the electric matter, (which, when the elec- 

 trification was very ftrong, I once obferved mine to 

 do) it fhould be baked * a little, which will prefentiy 

 prevent it. If it is heated too much, it will not re- 

 ceive electricity readily enough; and then the mo- 

 tion of the index will not correfpond with fufficienj. 



* Wanned a little, to dry off the damps, particularly from 

 -<ht i-i.'lfx. 



exictnefs,. 



