2 70 EudhuuUr.-^Jinpmved Elt^nmcfei: 



vent tlic abforptloii from continuing while aiiy gas remains wh'icli is proper to fupport 

 combuflion. 



If the fluid be common air, or vital air mixed with any other gas, the quantity of water 

 wlilch has entered the retort mult be accurately mcafured after the cooling. It rcprefents 

 the volume of air abforbcd. Care mufl be taken to cnclofe the remaining gas under the 

 fame preffiire, by plunging the retort to the level of the line at which the enclofed water 

 rells, before the orifice is flopped. 



This operation of meafuring, which is very eafy when meafuring vcfiels are at hand, may 

 be habitually performed by a flip of paper palled oo the neck of the retort, upon which divifions 

 are drawn from obfervation, and which muft be covered with varnifh, to defend it from the 

 aclion of the water. 



- IX. 



Defcription of an hnprovid Elf3rotncter, in tchich the SeiifiHI'ty of the Gold-Leaf is confiderohly 

 augmented, and the Iv.tenjities are dijlinguijlied by mimcrical Graduation, 



I 



T is fcarcely to be fuppofed that any philofofiher who is converfant with eleftricity caa 

 be unacquainted with the elecflrometer of Bcnnct, in which two pendent flips of gold-leaf 

 are fubllituted in the place of the pith-balls of (."anton, and ferve to indicate the nature and 

 quality of very minute intenfities of the ele£lric ftate. There are two particulars in which 

 this excellent inftrument appears capable of improvement : the firft, to render it portable, 

 without danger to the gold-leaf, and the fecond, to cxprcfs its various degrees of cleflriza- 

 tion by a fcale of divifions. 



1 have reflei5ted much on ihe probable means of fecuring the gold-leaf from fra£lure by car- 

 riage, but hitherto with little profpe£l of fuccefs. There was fome hope that a fingle flip of 

 this gold might be prcfervcd in a ihcath or box, with its fides very nearly in contadl ; but 

 when I placed fuch a flip upon a gilded piece of wood of the fame fuperficial dimenfions, to 

 which it was fadened at one end, its flexibility was fuch that the leaf very readily Aided along 

 the furface of the wood, and became full of folds, by inclining the faftened end a very few 

 degrees lower than the other extremity. There was dill lefs immediate expe£lation that the 

 flips could be actually and repeatedly confined between two leaves orculhions, as in the book 

 of the gold-beaters, without their being broken by occafional agitation. To this, however, 

 my attention will probably be direiled when I may again refume this objetl. In the mean 

 »ime, I recommend it to other philofophers, as a very defirablc improvement in the mine- 

 ralogical apparatus, and (liould rejoice to be anticipated by their fuccefsful rcfearchcs. 



The weight of one flip of gold-leaf, in the eleftrometer of Bennet, is about one-fix- 

 hundredth part of a grain ; but this, as well as the fenfibility of the inftrument, muft vary, 

 not only from the figure and dimenfions of the piece, but the nature and ihicknefs of the> 

 gold itfelf *. It feemcd, therefore, unneceflary to endeavour to render two of thcfe inftru- . 

 mcnts comparable with each other. All that could be done was, to diftinguifli the different 

 intenfities as fliewn by the divergencies of the leaf; or, as I have taken it, t!ie diftances at 



• Philofo]iliicul Journal, I. 133. 



6 wltich 



