Chemistry and Physics. 411 
required pacts ope in square inches, d the given distance in miles. 
In the smaller heliotropes the amount of light cut off by the 
favorable circumstances the image appears too bright, the area of 
the mirror may be readily reduced upon a preconcerted signal, by 
affixing an open — of tin or even of paper upon the outer 
edges of the mir 
14. On the Artificial Formation of the Diamond.—The last 
number of the Proceedings of the Royal Society (No. 201), 
pane a pees notice by Mr. J. B. Hannay of the process 
by which he seem ave succeeded in eee pp aera 
carbon identical wits ‘the diamond. The following is an extrac 
When the carbon is set free from the hydrocarbon in presence 
of a stable compound containing nitrogen, the whole being near 
a red heat and under a very high pressure, the carbon is so acted 
open in nine cases out of ten. 
“The carbon obtained in the successful experiments is as doesn 
as natural diamond, ounce all other'crystals, and it not 
affect polarized light. have obtained crystals with pean faces 
belonging to the ‘octahedral sand ne Huson is the only sub- 
stance ape ng in this man d ecific gravity is as 
hi The crystals burn anil on thin platinum-foil over 
& goo ble owpipe, and leave no residue, and after tw im- 
mersion in hydrofluoric acid the w n of di g, 
ey sho ; : 
even when boiled. On heating a splinter in the electric are, it 
diamond. 
n 
ignited by an electric current, and the combustion conducted in 
pure oxygen, The result obtained was that the sample (14 
mgrms.) co ntained 97°85 per cent of carbon, a very close approx- 
Imation, spushdaviag the small quantity at my disposal.” 
