his Thermometer with the common mercurial ones. 367 
eenter of an oven more than five hundred times its own capa- 
city, it could not well fail of being heated pretty uniformly, at 
leaft through the fmall {pace which thefe experiments re- 
quired; nor haveI found any reafon to fufpeét that it was not fo, 
. The gage being laid flat upon the bottom of the muffle, with 
the filver piece in the canal as before, fome of the clay ther- 
mometer pieces were fet on end upon ‘the filver. piece, with 
that end of each downwards which is marked to go foremoft in: 
meafuring i it; that is, they were in contaét-with the filver in’ 
that part of their furface by which their meafure is afterwards: 
afcertained. I was led to this precaution by an experiment I 
had made upon another occafion, in which a number of ‘ther- 
momieter pieces having been fet upright upon an ‘earthen-ware’ 
plate, over a fmall fire, till the plate became red-hot, all “the 
pieces were found dimmifhed, fome of them more than two: 
degrees, at the lower ends which refted uponthe plate, whilft 
the upper ends were as much enlarged, not having yet pafled the 
ftage of extenfion which, as obferved in the former paper, al- 
ways precedes the thermometric diminution : thusowe fee how’ 
pundtually every part of the piece obeys the heat that acts-upon it. 
_.'The fire about the oven was flowly. increafed for fome hours, ’ 
and kept as even and fteady as poffible, by.an experienced fire- 
man, under my own infpection. Upon opening a {mall door, : 
which had been made for introducing the apparatus, and look - 
ing in from time to time, it was obferved, that: the muffle, 
with the adjacent parts of the oven and ware, acquired a vifible . 
rednefs at the fame time; and in the progrefs of the operation, 
the eye could not diftinguifh the leaft diffimilarity in the afpe&: 
of the different parts ; whereas in {mall fires, the difference: not 
only between the two ends of the muffle, but in = lefs 
diftances, 1s fuchoas to ftrike the eye-at once. 
When 
