1 16 Injlrumenl for Mtafutiiig Sptci/ic Grav'tt'itt. 



i. It is more convenient to add a few milligrams to the conRant additional weight, than to 

 compofe a lefs by a feries of fub-multiples j 2. By making ufe of a liquid, at the teniperu- 

 ture of the furrounding air, it is evidently lefs expofcd to fuddcn variations. Thefc cir- 

 tumllances arc more favourable to accuracy in the refult. 



Explanation of thi Figures, 



Fig. 2, riate VI. — ^Thc gravimeter. 



a. The lower bafon. 



b. The upper bafon. 



c. The point of immerfion marked on a thin piece of glafs in the infide of 

 the flem. 



p;<T. 3. The piece called y>/5«^«/r, which is placed in the lovper bafon a when experiments 

 are made on fluids of greater denfity than water. 



Fig. 4. The gravimeter in the cylindric veflel filled with water, in which it floats, im- 

 merfed to the mark c, by means of the additional conftant weight d. 



It is convenient to choofe a veflel of fuch a depth that the inftrument may be at liberty to 

 float at the level of the mark, or even beneath it, without its being pofllble that the bottom 

 of the upper bafon (hould ever defcend to the furface of the water. 

 Fig. 5. The gravimeter in its cafe. 



A. The cylindrical part of the infl:rument lodged in a groove in the cafe, and 



fecured above by the two projeftions e e which leave the flem at liberty. It is 



fccured at the middle by the brafs button f, and is prefled below by a piece of 



cork g, which refts on the fixed block h. 



i. Sliding piece and fcrew to fupport the ballaft-piece, and prevent the branches 



from being endangered by any internal movement of the mercury. 

 k. The additional ballad-piece, or plongeiir in its feparate cell. 

 1. The conftant additional weight placed in a cell cut in the folid wood, and 

 cleared out at the fides, fo that it may be conveniently taken up when wanted, 

 m. The inner furface of the cover hollowed out at n to receive without friftion 

 the projefting part of the upper bafon. A. paper is parted on the inner furface 

 of the cover, to (hew the weight of the gravimeter with or without the ad- 

 ditional ballaft-piece, and the volume of water it difplaces in either cafe, which 

 are often required to be accurately known. 



On the ufeful Application of the Gravimeter to the Refults rf Tables of Specif c Gravity. 

 IT is frequently neccflary, in philofophical as well as commercial tranfaftions, to deter- 

 mine the proportions of a mixture of two liquids, or an alloy of two metals; and it has been 

 for fome time known, that in order to render this operation eafy and certain, recourfe 

 muft be had to tables drawn up from obfervation with the afliftance of an inftrument ca- 

 pable of giving the fpecific gravity to at leaft three* decimals. The gravimeter will perfeftly 

 anfwer this purpofe. To (hew this more efl^eftualty, I ftiall apply it to the mixture of 

 alcohol and water, and the alloy of tin and lead. Thcfe two compofitions are precifely 

 what in a commercial point of view moft frequently require to be examined in this refpeft. 

 And I am convinced that an exhibition of the moft accurate refults of experiments of fuch 



extent and minutenefs, cannot fail to prove acceptable in this place. 



A TABLE 



