26b philosophical transactions. [anno 1777. 



To avoid the inconvenience of this correction, perhaps it may be thought 

 tliat, both in adjusting the boiling point and in trying the heat of liquors, it would 

 be better that not much more than the ball of the thermometer should be im- 

 mersed, and that the tube should be held inclined in such manner as to be heated 

 as little as possible; as it may be said, that by this means you will find the heat 

 of liquors pretty nearly, without the trouble of making any correction; and that, 

 though in strictness a correction would be required in observing the heat of the 

 air with such thermometers, yet the heat of the atmosphere never differs so 

 much from the mean heat, as to make that correction of much consequence.* 

 But, on the other hand, this method of making and using thermometers is 

 much less exact than the former, and therefore is unfit for nice experiments; and 

 besides, a correction would be as necessary with this kind of thermometer in try- 

 ing the heat of air, artificially heated, or in finding the heat of large quantities 



meter in the usual manner, and heat the ball till there is a proper quantity of quicksilver in the tube, 

 and then to make die colimin of quicksilver separate at the neck of the ball, and mn to the extre- 

 mity of the tube, so as to leave a vacuum between the ball and the column of quicksilver, as is ex- 

 pressed in tig. 12, where the shaded part ad represents the column of quicksilver, and ba that part 

 in which tliere is a vacuum. The tube must then be sealed somewhere between b and a, as at e, 

 and cut off tliere ; after which it must be held witli the end d upwards, so as to make the column of 

 quicksilver run to tlie extremity e : by this method of filling, it is plain tliat no sensible quantity of 

 air can be left between e and the column of quicksilver ; but yet the quicksilver will be apt not to 

 run sufficiently close to the extremity k, as the weight of the column wiU be scarcely sufficient to 

 force it into the narrow space which will commonly be left in sealing the tube, especially when held 

 nearly horizontal : for this reason it will be proper to open the tube at d, so as to let in the air, and 

 then seal it again. It must be obser\'ed, that tlie space left between d and the column of quicksilver, 

 ought not to be less than the lOtli part of the length of the column of quicksilver ; as otherwise the 

 included air might be too much compressed by the expansion of tlie quicksilver when much heated. — 

 Orig. 



* The degrees on all thermometers are intended to ans\\er to equal portions of the solid contents of 

 the tube ; and consequently, if tlie quicksilver in the tube is kept constantly of the same heat as that 

 in the ball, the degrees w'Jl answer to equal increments of bulk of the whole quantity of quicksilver 

 in the thermometer, that is of a given weight of quicksilver. But if only the quicksilver in tlie ball 

 is heated, and tliat in die tube is kept always of the same heat, the degrees will answer to equal incre- 

 ments of a given bulk of quicksilver; so that the scale of die thermometers will be really different 

 in these two methods of proceeding, and in high degrees die difference will be very considerable : for 

 example, let two thermometers be made, and in the first of diem let care be taken, both in adjusting 

 the fixed points and in trying the heat of liquors, diat the quicksilver in die tube shall be of the same 

 heat as that in the ball ; and in adjusting the fixed points of the 2d, and in trying the lieat of liquors 

 with it, let care be taken diat the quicksilver in die tube shall remain always of the same invariable 

 heat, and let the freezing and boiling points be marked 32 and 212 on bodi of diem: then will die 

 defjree of (i20 on die 1 st answer to diat of 6OO on die 2d ; diat of 400" to 400 ; diat of 302 to 300 ; 

 and that of 1 iy.7 to 120; that i.s, a liquor which appears to be of 6'20° of heat by the 1st, will ap- 

 pear to be of 600" by die 2d, &c. It hence appears, that it would be improper to employ the latter 

 method of adjusting and using diermometers for ordinary purposes, and the former for nice experi- 

 ments. — Orig. 



