VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 50] 



air, but also by causing, at the same time, a greater or less quantity of moisture 

 to remain attached to the glass. 



To remedy these evils, and also to render the experiment more striking and satis- 

 factory in other respects, I proceeded in the following manner. Having provided 

 3 bottles a, b, and c, as nearly alike as possible, and resembling in all respects 

 those already described; into the first, A, I put 4214.28 grains of water, and a 

 small thermometer, made on purpose for the experiment, and suspended in the 

 bottle in such a manner that its bulb remained in the middle of the mass of water; 

 into the 2d bottle, b, I put a like weight of spirit of wine, with a like thermometer; 

 and into the bottle c I put an equal weight of mercury. These bottles, being all 

 hermetically sealed, were placed in a large room, in a corner far removed from the 

 doors and windows, and where the air appeared to be perfectly quiet; and being 

 suffered to remain in this situation more than 24 hours, the heat of the room (6l°) 

 being kept up all that time with as little variation as possible, and the contents of 

 the bottles a and b appearing, by their inclosed thermometers, to be exactly at the 

 same temperature, the bottles were all wiped with a very clean dry cambric hand- 

 kerchief; and being afterwards suffered to remain exposed to the free air of the room 

 a couple of hours longer, in order that any inequalities in the quantities of heat, 

 or of the moisture attached to their surfaces, which might have been occasioned 

 by the wiping, might be corrected by the operation of the atmosphere by which 

 they were surrounded, they were all weighed, and were brought into the most ex- 

 act equilibrium with each other, by means of small pieces of very fine silver wire, 

 attached to the necks of those of the bottles which were the lightest. 



This being done, the bottles were all removed into a room in which the air was 

 at 30°, where they were suffered to remain, perfectly at rest and undisturbed, 48 

 hours; the bottles a and b being suspended to the arms of the balance, and the 

 bottle c suspended, at an equal height, to the arm of a stand constructed for that 

 purpose, and placed as near the balance as possible, and a very sensible thermometer 

 suspended by the side of it. At the end of 48 hours, during which time the appa- 

 ratus was left in this situation, I entered the room, opening the door very gently, 

 for fear of disturbing the balance; when I had the pleasure to find the 3 thermo- 

 meters, viz. that in the bottle a, which was now inclosed in a solid cake of ice, 

 that in the bottle b, and that suspended in the open air of the room, all standing 

 at the same point, 29° f, and the bottles a and b remaining in the most perfect 

 equilibrium. To assure myself that the play of the balance was free, I now ap- 

 proached it very gently, and caused it to vibrate; and I had the satisfaction to find, 

 not only that it moved with the utmost freedom, but also, when its vibration ceased 

 that it rested precisely at the point from which it had set out. 



I now removed the bottle b from the balance, and put the bottle c in its place; 

 and I found that that likewise remained of the same apparent weight as at the be- 

 ginning of the experiment, being in the same perfect equilibrium with the bottle 

 A as at first* I afterwards removed the whole apparatus into a warm room, and 



