the Production of artificial Cold . 131 
be used with this apparatus, should be so long as just to pass 
through the bottom of the tube a , viz. -J of an inch below it. 
Fig. 2, represents the spirit thermometer made use of in the 
experiments : it consists of three parts, viz. A is the thermo- 
meter, having its scale-board (made of box-wood) of a semi- 
cylindrical form, being flat in front, and round at the back, in 
order that it may be adapted to the cylindrical tube B B, in 
which it slides easily up and down, centrally; and may be 
occasionally taken out of it. C, is a brass ferrule, cemented to, 
and forming one piece with, the tube, having a top or cover, 
which screws off and on. The scale extends from 100 be- 
low o, to 100 above o ; the scale upwards being carried so far 
only as to allow of the unavoidable expansion to which the 
spirit may be subjected by atmospheric heat. 
The thermometer (contrived by myself, and very accurately 
and neatly executed by Mr. Nairne, philosophical instrument- 
maker, in London,) is exactly tzvice the dimensions of the re- 
presentation in the drawing, (as the scale,) and is graduated to 
single degrees ; it has a common case, to make it portable. 
N. B. A thermometer of the size described, is equally fit for 
an apparatus on a larger or smaller scale than that repre- 
sented in Fig. 1. 
The apparatus is used thus. The two vessels being taken 
apart, 1st. A circular piece of writing-paper is cemented* over 
the bottom of the tube a. 2d. A frigorific mixture-f is made 
• I use mucilage of gum arabic, or butter, if the other be not at hand ; but it is 
sufficient merely to dip the paper in water, and apply it ; the effect of the freezing 
mixture quickly cementing it. 
t A frigorific mixture, according to the intention, may be selected from the table in 
P a £ c 1 35 °f this paper ; or, in defect of ice, from the table in page 279 of Phil. Trans. 
S 2 
