Mr. J. Herapath on the Indications of Tliermometers. 9 



50° Fahr. gradually into mercury at about 350°. After the 

 thermometer had risen as high as it would, I took it out, and 

 rapidly cooled down the bulb by means of a wet cloth to 

 within about 50° or 70° of 212°. Plunging the bulb im- 

 mediately into water rapidly boiling, I observed the mercury 

 descend to a certain point ; and then regularly, but somewhat 

 quickly, rise and settle from a degree to a degree and a half 

 higher. I could not ascertain the exact ascent, in consequence 

 of the divisions of the scale comprehending each not less than 

 two degrees. 



Exp. 2. Having first cooled down the stem and bulb, by 

 immersing the instrument for some time in water of about 50°, 

 I put the thermometer as before into mercury of 400° or up- 

 wards. Suffering it to become stationary, it was taken out, 

 and the bulb cooled, by similar means to that in the last ex- 

 periment, to about 300°, and then immersed in the same water 

 boiling very fast; a like rise took place, after the mercury had 

 sunk to its minimum, but as I fancied a little greater ap- 

 proaching nearer to two degrees. 



An accident at the close of this experiment unfortunately 

 destroyed the thermometer I used, which happened to be the 

 last I had left that extended to a high range. This prevented 

 me from trying other similar experiments on a more careful 

 and varied plan. 



The instrument ranged from about — 100° to nearly + 500° ; 

 and its bulb extended 3-4ths of an inch or more below the scale. 



After the lapse of a considerable period, I recollected that 

 I had a thermometer by me, which, though not very good for 

 measuring great intervals of temperature, on account of the 

 irregularity of its calibre, was nevertheless, from its sensibility 

 and range, well suited for delicate experiments of this kind. 

 It extended from about —44° to -f-106°, and was so sensible, 

 that the temperature might be read off to the 1-1 5th of a de- 

 gree, or even to the l-30th with great care. Its bulb projected 

 three inches beneath the scale. 



With this instrument I made the following experiments * : 



Exp.7. Leaving my thermometer and 16865 grains of mer- 

 cury in a glass tumbler, weighing 2835 grains, for about twelve 

 hours in the same room, I took the temperature of the mercury 

 at 51 0- 27, the air being 52°. Putting the bulb immediately af- 

 terwards in water of a much higher temperature, I allowed the 

 thermometer to ascend to 105°. As I could not safely venture 

 to raise the mercury higher, I took out the instrument, suffered 

 it to cool a few degrees, and then reimmersed it. This I did 



* The intermediate experiments, and the 1 Ufa, hare been struck out by 

 the author for the sake of brevity ; but their mean results are included in 

 the general balance. 



Vol. 63. No. 309. Jan. 1824. B two 



