Ill Kfio Jujlrumfnl for Afea/iir'iHg Sptdjii; Gravit!ft. 



and conftittiting difltreht ballads; but this did not anfwcr in every reTpeift. In all 

 the inllrumeius of tliis kind which I have had occafion to examine, no attempt had been made, 

 or at Icall the object had not been accompliflicd, to render the point of iiiterfeiSion of the 

 item with the fluid, common to all the ballads. Whence it followed, that, upon changing 

 the ballad, it was litcewife ncceflary to change the flip of glafs which carries the maik 

 within the upper ilem. 



I have thought it pofliblc, by following the principles of Fahrenheit and executing the 

 inftrument of Nicholfon in glafs with a flight addition, to render it more generally ufeful 

 nnd commodious, without diminifliing its accuracy in any refpeil. I was well aware of 

 the prejudice which is naturally entertained againd polychrell, or univerfal indruments, 

 mod of which are rendered of no ufe from the attempt to extend their application too far; 

 but at the fame time I was convinced that it would be a real advantage to every pliiiofophical 

 obfervcr, to require only one fingle meafure for determining the denfity of all bodies, 

 whether folid or liquid. This is the objeil I propofe to accomplifti. It will be feen how 

 far I have fueceeded. I mud obferve, on this occaGon, that the name hydrometer ffeje- 

 liqueur) as well as that of areometer, is fcarcely applicable to an indrument polTefling thefe 

 qualities; for thefe terms fuppofe that the liquid is always the thing weighed; uhercas, 

 with regard to folids, the liquid is the term of comparifon which is known, and to wliich the 

 unknown weight is referred. I propofe therefore to make ufe of the name gravimetcr, 

 which will eafdy be underftood, and applied with propriety in every cafe. 



This indrument, being executed, as already remarked, in glafs, is of a cylindric form, 

 being that which requires the fmalied quantity of the fluid, and is on that account pre- 

 ferable, except fo far as it is neceflary to deviate for the fecurity of a perpendicular pofition. 



Like the indrument of Nicholfon, it carries two bafons ; the one fuperior, at the extremity 

 of a thin dem ; towards the middle of which the fixed point of immerfion is marked. 

 The other lower bafon terminates in a point ; it contains the ballad, and is attached to the 

 cylinder by two branches. The moveable fufpenfion by means of a hook has tlie incon- 

 venience of ftiortening the lever which is to fecure the vertical polition. 



The cylinder is 22 millimeters (0.71 inches) in diameter; and 21 centimeters (6.85 

 inches) in length. It carries in the upper bafon an additional condant weight of five 

 grammes. Thefe dimenfions miglit be increafed, fo as to render it capable of receiving a " 

 much more confiderable weight; but it will hereafter be fhewn, that this is unneccfliiry. 



I have added a piece which I call the diver (plongeur), becaufe in faft it is placed in the 

 lower bafon when ufed, and confcquently is entirely immerfed in the fluid *. It is a bulb 

 of glafs, loaded with a fufficient quantity of mercury, in order that its total weight may be 

 equal to the condant additional weight, added to the weight of the volume of water dif- 

 placed by this piece. 



It will readily be underdood, that the weight bring determined at the fame temperature 

 at which the indrument was originally adjuded, it will fink to the fame mark on the dem, 

 whether it be loaded with a condant additional weight in the upper bafon, or whether the 

 eflxft of this weight be produced by the additional piece in the lower difh. 



From this explanation there will be no difliculty in deducing how this indrument may 

 be adapted to every cafe of praftice. 



* As we have no word in the EngliOi language which can with propriety be ufed as the tranllation of the 

 word plongeur, I (hall take the liberty to call this weight the additional piece. N. 



It 



