Experiments refpccl'ing Heat. $2$ 



The tub ABCD, three feet high and fixteen inches and a 

 half internal diameter, is made of mahogany, and reds on a 

 low (land. A large glafs receiver E, open at the bottom, 

 nearly fills the diameter of the tub. This receiver is twenty- 

 two inches in height from the lower edge to the crown, 

 about fixteen inches internal diameter, and is capable of 

 containing about ten gallons of gas : it afcends or defcenda 

 in the tub, guided bv the rod FG attached to its top, and 

 palling through the crofs-bar HI. In this crofs-bar there is 

 fome fimple wheel-work worked by the pulley at L (concealed 

 in the crofs-bar), and which, turning an index, tells the 

 quantity of gas expended from time to time, when that cir- 

 cumstance is wiflied to be noted. The pulley at L is worked 

 by the chain KL attached to the top of the receiver. From 

 the pulley at L this chain paries to the pulley M, where it is 

 wound up or let oft" at pleafurc by means of weights put into 

 the fhell N, or removed thence to the horizontal plate O, 

 which", bv means of a focket, may be either put on or taken 

 from the top of the rod FG. This contrivance is for the 

 purppfe of enabling the operator to command the prefmre of 

 any required column of water which the tub can contain, 

 which is therefore made deeper than the receiver. To faci- 

 litate this, the pulley M has two grooves on its circumference, 

 one of which receives the chain KL, and is eqUi-diftant from 

 the centre all round ; the other, which receives the cord to 

 which the fcale N is attached, is not equi-diftant from the 

 pivot, but in a fnail form, fo adjufted as, with a given weight 

 in the fcale X, to counterpoise exactly the glafs receiver E, 

 •whether wholly or partiallv immerfed in the water in the tub ; 

 Co that, when no weight is on the round plate O, the height 

 of the water within and outfide of the receiver will be on a 

 level; in other words, no prelfure will be exerted on the gas 

 it contains. Bv then putting known weights on the plate O, 

 the receiver is prefied down in the water fo as to maintain 

 an uniform prefiure of any required column of water during 

 thc whole tune of the procefs. 



The gafometer i: : charged in the following maimer: — . 



Water is lirit poured into the tub ABCD (till full if necef- 



. ct of couric afcends (no weight being then 



on 



