for measuring the higher Degrees of Pleat, he. 32T 
diminution of their bulk by being re-pafled through degrees of 
heat which they have already undergone, but are diminifhed 
by any additional heat (according to Obf. V.), if a fragment 
of them be made to fit into any part of the gage, and then 
fired along with a thermometer-piece till it begins to diminifh* 
the degree at which this happens points out the heat by which 
it had been fired before. Of feveral pieces of ancient Romd« 
and Etrufcan wares, which I have examined, none appear to 
have undergone a greater heat than 32°, and none lets than 
20 0 ; for thev all began to dkninifh at thole or the intermediate 
7 J O 
degrees. 
By means of this thermometer feme interefling properties of 
natural bodies may likewife be difeovered or more accurately 
determined, and the genus of the bodies afeertained. Jafper, 
for inftance, is found to diminifh in the fire, like an artificial 
mixture of clay and filiceous matter ; granite, on the contrary, 
has its bulk enlarged by fire, whilft flint and quartzefe flones 
are neither enlarged nor diminifhed. Thefe experiments were 
made in fires between 70 and 8o° of this thermometer. A fuf- 
ficient number of fads like thefe, compared with each other, 
and with the properties of fucli natural or artificial bodies as 
we wifh to find out the compofition of* may lead to various 
difeoveries, of which I have already found fome promifing 
appearances ; but many more experiments are wanting to ena- 
ble me to fpeak with that certainty and precifion on thefe 
fubjeds which they appear to deferve. 
A piece of an Etrufcan vafe melted completely at 33 ; 
pieces of fome other vafes and Roman ware about 36°; Wor* 
cefler china vitrified at 94 0 ; Mr. sprimont’s Chelfea china 
atio5°; the Derby at 1 1 2° ; and Bow at 12 1°; but Briftol china 
flie wed no appearance of vitrification at 135 0 . The common fort 
Vol. LXX 1 L U u of 
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