434 ^-"^ '^* Hydrometer, 



the various temperatures, and indicated ^6 gradations of 

 ftrength. I perceived, therefore, tliat the principle would 

 anfwer, but that it could be improved ftill furtiier; and after 

 \'arious efforts I at lengsh fixed on that conftruction, of which 

 1 ftiall now beg leave lo give a defcription. 



This now hydrometer is made of hard brafs : the ball is 

 (haped in the form of a pear, being nearlv two inches in dia- 

 meter at its greateft dimenfion, and two inches and a quarter 

 in length : the lower Item meafurcs one inch and a half, and 

 is in Ihape a prifm, each fide mealuring one-eighth of an 

 inch : to the lower end of this a round weight is fixed, the 

 diameter of which is feven-eighths of an inch. The upper 

 fiem is in length five inches and a half, and is an ot'-.fagon, 

 each fide being fomewhat lefs than an eighth ot an inch 

 wide : each of thefe fides is graduated for a temperature en- 

 graved on the top, the loweft being cj^, the fecond 40, and 

 lb increafing by five until it reaches 70. The ^.err^ or proof 

 point, is marked 0, and the gradations of ftrength (numbered 

 at every fourth) amount to fixty-fix, and thofe fo clearly di- 

 ftindlj that at the over-proofs they will admit of a fub-divifion, 

 and by. that means indicate a half per cent. Thefe divifions 

 are not at equal diftanccs; an error which takes place in the 

 prefent IrifVi and feveral of the old hydrometers, but widen 

 in proportion as the fpecific gr-ivity of the fpirit diminifliesj 

 and, being graduated with fpirits of known ftrengths at every 

 four per cent., the intermediate per cenuiges are adjulled by 

 interpolation. 



To prevent any error which might arife from taking the 

 indication of ftrength from the wrong fide of the ftem, an 

 index is applied on the top of it, with an opening to lliow 

 the figures which point out the temperature. This ia^flex, 

 which aiiplics merely to the purpofe here mentioned, n.ay be 

 removed lower to any part of the fiem, but above the furface 

 of the liquor, without aliening the accuracy of the initru- 

 ment, as neither its weight nur dimenfion is changed ; and 

 being of a difierent colour from the ftem (fanguined fteel) it 

 forms a contraft with it, and, as it were, points to the indi- 

 cation fought for, by which every danger of error in this re- 

 fpf Ct is removed. 



Although this is the only ufe of the index, when the tem- 

 perature fliall be found one of thole eight marked on the ftem, 

 vet it is neceflary that the iulirument fiiall accord w ith the 

 four intermediate degrees between each of the adjoining fiilcs: 

 for this purpolc one of two other indexes of difterent vvciglits 

 art occalionallv fubftitutcd for the firft oiie, in order to lighten 



the 



