on the Combu/ftion of the Diamond. 64 
I thought it might be of fome importance to preferve the 
fubject of thefe obfervations, and that it would not difgrace 
the collection of the cabinet of the School, with an infcrip= 
tion allufive to the experiment to which it had been fub- 
jected. “Another diamond: was therefore deftined to be put 
nto the apparatus, in order that it might be there fubje&ted 
to entire combuftion. This diamond was alfo a pretty regular 
oétaedron, of a much more beantiful water than the pre~ 
ceding, and weighing 209"1 milligrammes, 3°77 grains. 
As the feafon was already fo far advanced that it left us 
no hope of a folar focus as ftreng as that from which we had 
obtained fo little effect with the lenfes we had employed, I 
was defirous of terminating the experiment with the great 
Jens of Tfchirhaufen; and the clafs granted me permiffion 
to také it from their cabinet, 
This lens,° as is well known, is 86:6 centimetres (32 
inches) in diameter, and 211°076 (73 inches) focus. We 
augmented its power {till more by catching the luminous 
cone with the {mall lens of the cabinet of the Inftitute, the 
ditk of which is 37°89 centimetres, and the focus 56°83, 
which in this pofition was fhortened to 5°41 centimetres. 
A firft fitting gave fcarcely any figns of a commencement 
of combuftion. Next morning, the luminous difk having 
fallen on one of the parts of the bell which was thickeft, it 
occafioned it to crack. It was therefore no longer poflible 
to compare the volume of the gas before and after the ope- 
ration, nor to diftimguifh and afcertain the quantities of the 
products. We confined ourfelves to making lime-water pafs 
through the interior of the bell before the fiffure had fuffered 
a fenfible quantity of common air to enter, and we obferved 
that it was much troubled. 
The diamond which had been laft expofed was noways 
changed at its furface: it had, however, loft two decimilii- 
grammes of its weight; which was verified by the fame 
balance with which it had been weighed, and which is ca- 
pable of marking, in a very fenfible manner, thefe fractions 
of the milligramme. Thus we were obliged to adjourn the 
experiment till the next fummer, in order to find a more 
favourable fun, and to have time to provide a new apparatus, 
[To be continued, | 
XIII. Account 
