264 PHILOSOPHICAL TRANSACTIONS. [aNNO 1777. 



same in both cases. In the other short thermometer, as there were only half as 

 manv degrees to an inch, the error was only half as great. 



In several of the experiments however we made use of the long thermometer; 

 but then it was necessary to make an allowance on account of tlie quicksilver in 

 the tube being not heated equally with that in the ball. The better to enable us 

 to do this, we made use of a thermometer tube, filled with quicksilver in the 

 same manner as a thermometer, only without any ball to it, or a thermometer 

 without a ball, as we may call it. A small brass plate was fixed to the tube near 

 the top of the column of quicksilver, to show the heat, as in a common ther- 

 mometer. In all our experiments with the long thermometer in open vessels, 

 this tube, without a ball, was placed by its side ; whence, as the quicksilver in 

 the tube of the long thermometer could hardly fail of being nearly of the same 

 heat as that in the tube without a ball, we knew pretty nearly the heat of the 

 quicksilver in the tube of the former, and consequently how much higher it 

 would have stood if the quicksilver in its tube had been of the same heat as that 

 in the ball. For example, on October IQ, the long thermometer tried in an 

 open vessel, the water boiling fast, stood l^.fis Iov\er than it did when tried in 

 steam the same day, the quicksilver in the tube without a ball standing at the 

 same time at 109°: we may therefore conclude, that the heat of the quicksilver, 

 in that part of the tube of the long thermometer which was not immersed in the 

 water, was also 109°; and consequently, as that part of tiie tube contained 



about 170°, the thermometer stood -^-rrTT^Q—i •->•■ 1°^^ lower than it would have 

 done if the quicksilver in the tube had been of the same heat as that in the ball ; 

 and consequently the quicksilver in the ball of the thermometer was in reality 

 .07 cooler than when tried in steam. 



We examined the boiling points of several thermometers, made by different 

 artists, by trying them in steam when the barometer was at 30.1, and finding 

 what division on the scale the quicksilver stood at. The difiierence of the ex- 

 tremes was 3°Ji-; but, by a mean of all, it was found to stand at 213°.l, and 

 consequently would have stood at 211°, if the barometer had been at 29.4 ; so 

 that if the boiling point was to be adjusted, either in steam, when the baromete 

 is at 29.4, or with the ball immersed 2 or 3 inches in water, when the barometer 

 is at 29.1, it would agree best with the mean of tlie abovementioned thcrmo 

 meters. But as it seems to be of no great signification to make the boiling- 

 point agree very nearly with the mean of the thermometers made at present, 

 when the extremes differ so widely ; and as we apprehend that it will be more con- 

 venient to the makers that some height should be chosen which differs less from 

 the mean, as thus tliey will more frequently have an opportunity of adjusting 

 the boiling point without the trouble and danger of mistakes which attend the 



