148 Experiments made at the Polytechnic School 
tres (28 inches), and to the mean temperature of 12°5 de- 
grees of the decimal thermometer, according to the experi- 
ments of.Cit. Pneier, and the tables of Cit. Prony*, was 
then found to be 11,470 cubic centimetres. 
Having taken the neceffary precautions to heat gradually 
the balloon, the point of the luminous cone being ,almoft in 
the centre, we were obliged to cover with a glafs plate the 
wooden fupporter, which was already on fire. The diamond 
firft exhibited a black point at the angle immediately ftruck 
by the fun. We afterwards faw it entirely black, and as it 
were charred: we diftinctly perceived, a moment after, bril- 
liant points in a ftate of ebullition, as it were, on the black 
ground. The folar rays, having been for a moment inter- 
cepted, it appeared tranfparently red. The fun becoming 
obfeured by a cloud, we faw it of a much purer white chan 
it had been at the commencement of the operation. 
The fun having emerged from the cloud, the furface of the 
diamond affumed the appearance of metallic fplendour: it 
was then fenfibly diminifhed, and there remained no more 
than a quarter, of a len¢thened form, without angles or per- 
ceptible edges, but ftill very white, and of a beautiful tranf- 
parency. We obferved a flight fiffure at the bottom of the 
pipe which fupported it, but without any feparation of the 
parts. I muft not forget, that at the commencement of the 
combuftion we thought we obferved a purpurefcent cone arifing 
from the fupport in the pencil of the folar rays; but this phe- 
nomenon was only an optical effet, which depended on the - 
pofition of the obferver. 
The whole apparatus was left j in the fame ftate, only de- 
fended by an inverted box placed over it, until the 7th, when 
we again began, at one hour twenty minutes, to prefent the 
diamond to the focus. We foon obferved the fame pheno- 
mena as on the 5th, the black furface, the brilliant points in 
ebullition, which vanifhed and re-appeared according to the 
intenfity of the focus: we faw alfo a brilliant metallid ap- 
pearance, or rather leaden-colour. This is the expreffion 
which the affiftants employed to charaéterife this phenome- 
non. At one hour forty minutes the diamond was entirely 
* Journal Polytechnique, Part IJ, p. 65. : 
confumed.' 
