VOL. LXriI.] PHILOSOPHICAL TRANSACTIONS. 26? 



will be affected by the steam of the liquor, and the fire by which it is heated, it 

 will commonly be of a very different heat from the rest of the air of the room in 

 which the experiment is made ; but as no great nicety is required in estimating 

 the heat of the quicksilver in the tube, insomuch that a mistake of 25° in it will 

 cause an error of only 4 a degree in the correction, when the number of degrees 

 in that part of the tube which is not immersed in the liquor is not more than 

 220°, it will commonly be not difficult to guess at the heat of the quicksilver in 

 the tube as near as is required.* But if the observer is desirous of more accu- 

 racy, he may find the heat of the surrounding air by holding the ball of a small 

 thermometer near the tube of the thermometer with which he tries the heat of 

 the liquor ; or, what will be much better, he may have a tube without a ball, 

 such as is above described, fastened to the frame of the thermometer, on one 

 side of the tube ; or if he has 2 such tubes, of different lengths, it will be still 

 more accurate. 



observed. The piece of wood was tlien removed, and the end of the tube laid in the sand, which 

 was heaped over it so that about half an inch of the column of quicksilver was entirely surrounded by 

 (he hot sand, and must therefore be heated to nearly the same degree as it. The quicksilver in the 

 tube rose very little higher than before, and seemingly not more than might be owing to the expan- 

 sion of the half inch of quicksilver which was surrounded by the sand ; so that it should seem, that 

 heating one end of the column of quicksilver does not communicate much heat to the rest of the 

 column ; and consequently, that when the ball of a thermometer is immersed in hot liquor, the 

 quicksilver in the tube wiU not be much hotter than the surrounding air. — Orig. 



* The better to enable the reader to guess at the heat of the quicksilver in the tube, in cases of 

 this kind, we tried how much the quicksilver in the abovementioned tube, without a ball, would be 

 heated when held over a vessel of boiling water. It is true, that these experiments catmot be of any 

 great service towards this purpose, as the tubes will be very differently heated, according to the de- 

 gree of heat of the fluid, and tlie quantity of steam which it flirnishes, and according to the nature 

 of the fire by which it is heated ; yet as tlie experiments may perhaps serve in some measure to rectilj^ 

 our ideas on this head, we will give the result. When the abovementioned tube without a ball, the 

 length of the column of quicksilver in which was 15 inches, was held perpendicularly over the 

 vessel of boiling water, with its bottom even with tlie surface of the water, the heat of the quick- 

 silver was in all the trials we made from 68 to 28° hotter tlian the air of the room. If the tube was 

 held inclined to the horizon, in an angle of about 30^, with tlie bottom of the column of quicksilver 

 reaching not more than tliree-quarters of an inch within the circumference of the pot, so tliat the 

 column of quicksilver was as little heated by the steam as could easily be done, it was from 30 to 7 "^ 

 hotter than the air. When a shorter tube of the same kind, in which the column of quicksilver was 

 7 inches, was used, the quicksilver was from 6'2 to 44° hotter than tlie air, when held perpendicularly, 

 and from 49 to 36° hotter when held inclined. The water in these trials frequently boiled pretty fast, 

 but never very violently. It was in general heated over a portable black lead furnace placed in the 

 middle of the room ; but it was once heated over an ordinary chafing-dish, when the quicksilver in the 

 long tube, held perpendicularly, was found to be 64" hotter than tlie air. When the experiments 

 were tiied without doors, the heat of the quicksilver in the tube would vary very much, according as 

 the wind blew the steam and hot air from or towards the tube, but it sometimes rose as high as it did 

 within doors. 

 The most convenient method we know of making these tubes without a ball, is, to fill a thi.-rino- 



M M 2 



