VOL. LXVII.] PHILOSOPHICAL TRANSACTIONS. 26 1 



sensible difference whether the water boiled fast or slow: but whenever there 

 was any, the greater height was when the water boiled fast: the difference however 

 never amounted to more than -jV "^ a degree. There was scarcely ever any 

 sensible difference whether the short thermometers were tried in the .short pot 

 or the deep one, though in the former case the ball was raised very little above 

 the surface of the water, and in the latter not less than 14 inches: neither did 

 we find any sensible difference in trying thein in the tall pot, whether there was 

 a greater or less depth of water in the vessel. 



As it was however suspected, that the heat of the steam might possibly be less 

 near the top of the pot than lower down (for in these experiments the ball of 

 the therinometer was always at the same depth below the cover, though its 

 height above the surface of the water was very different) we made 2 holes in the 

 side of a pot 4 inches deeper than the deepest of the foregoing, one near the 

 top of the pot, and the other not far from the bottom, and passed the ball of 

 the thermometer through one or the other of these holes, taking care to stop up 

 both holes very carefully, so that no air could enter into the pot by them: no 

 sensible difference could be perceived in the height, whether the thermometer 

 was placed in the upper or lower hole, though in one case the ball was only 3 

 inches, and in the other 21 inches, below the cover. The heat of the steam 

 therefore appears to be not sensibly different in different parts of the same pot; 

 neither does there appear to be any sensible difference in its heat, wliether the 

 water boil fast or slow; whether there be a greater or less depth of water in the 

 pot ; or whether there be a greater or less distance between the surface of the 

 water and the top of the pot; so that the height of a thermometer tried in 

 steam, in vessels properly closed, seems to be scarce sensibly affected by the 

 different manner of trying the experiment. 



Though there was scarcely any difference in the height of the quicksilver, 

 whether the water boiled fast or slow, yet, when the water boiled slow, the 

 thermometer was a great while belbre it rose to its proper height; and when it 

 boiled very slow, it seemed doubtful whether it would have ever risen to it, 

 especially if the ball was raised a great way above the surface of the water: but 

 when, by making the water boil briskly, the thermometer had once risen to its 

 proper height, the water might then be suffered to boil very gently, even for a 

 great length of time, without the thermometer sinking sensibly lower.* 



All 3 thermometers were found to stand, in general, from 30 to 65 hundredths 



* The reason of tliis seems to be, that, while any air is left in tlie pot, tlie steam cannot acquire 

 its lull degree of heat ; and tliat when the water boils very gently, the air is not easily quite expelled 

 from the pot. That the steam will not acquire its foil degree of heat while any air is left in the pot, 

 will appear from the next paragraph but onf. 



