3°^ An Attempt to make a \ Thermometer 
much uniformity and regularity as poffible, for near fixty 
houis. I he pieces, taken out at equal intervals of time during 
tins hicceflive increafe of heat, and piled in their order upon 
one anothei in a glafs tube, exhibited a regular and pretty ex- 
tenlive femes of colours ; from a fie decolour to a deep brownifta* 
lea, hom tnence to a chocolate, and lo on to nearlv black, 
with all the intermediate tints between thefe colours. * A back 
bang iixed to the tube, like the lcale of a thermometer, and the 
numbeis of the pieces marked upon it relpeftively oppofite to 
them, it is obvious, that thefe numbers may be confide red as 
fo many thermometnc div.ifions or degrees ; and that, if ano- 
ther piece of the lame competition be bred in any other kiln 
Oi furnace, not exceeding the utmoff heat of the brff, it will 
acquire a colour correlponding to lome of the pieces in the 
tube, and thus point out the degree of heat which that piece, 
and confequendy fucli other matters as were in the fire along 
with it, have undergone. 
It muff however be con felled, that, for general life, a ther- 
mometer on this principle is liable to objection, as ideas of co- 
lours are not perfectly communicable by words ; nor are all 
eyes, or all lights, equally adapted for diitinguifhing them, 
especially the Shades which approach near to one another ; and 
the effe&s of phlogiftic vapours, in altering the colour, may 
not in all cafes be eafily guarded againfL 
In considering this Subject attentively, another property of 
argillaceous bodies occurred to me ; a property winch obtains, 
in a greater or lei's degree, in every kind af them that lias come 
under my examination, io that it may be deemed a diitinguifh- 
ing chaiactei of this order of earths : I mean, the diminution of 
their bulk by fire ; I have the Satisfaction to find, in a courfe 
5 of 
