246 
7. It may be useful to condense into the form of a table the 
previous observations : — 
Forms of 
Carbon. 
Experiment. 
Calculations. 
Diamond, 
Graphite, 
Charcoal, 
Sp. Gr. Powers. 
3*46 or 3’48 2 = 12*11 
2*29 3 = 12*00 
1'88 4 = 12*49 
G Roots. 
V 12 = 3*464 
Xf 12 = 2*289 
V 12 = 1*865 
These relations appear to be so simple, that it is scarcely possible 
to conceive that they may not have been described before ; but I 
have been unable to find such descriptions. The nearest approach 
to it which I know, is the fact that Mr Hawksley, the engineer, 
stated to me, many years since, that he had brought under the 
attention of the late Mr Cooper the relation which seemed to sub- 
sist between the specific gravities of silver and gold and their atomic 
weights, this being approximatively the square root of their atomic 
weights, or of multiples of these numbers. But I cannot find any 
record either of Mr Hawksley’s or Mr Cooper’s views on the subject. 
8. We know two other bodies besides carbon which possess 
diamond, graphite, and amorphous forms— -viz., Silicon and Boron. 
If the same relation were observed between the specific gravities and 
atomic weights of these bodies, it would go far to establish as a law 
what, in an isolated case, might be due to a remarkable combination 
of chances. Unfortunately, we know only the specific gravity of the 
diamond forms of these elements : — 
Silicon diamond, . . 2 '49 Deville. 
Do., mean on six specimens, 2*48 Playfair. 
In quoting these results some explanation is necessary. In the 
original memoirs of Deville, it is left uncertain whether he examined 
the specific gravity of diamond or graphite silicon ; and manuals of 
chemistry give it as the result due to the latter form ; but from its coin- 
cidence with my own experiments on diamond silicon, it must unques- 
tionably refer to that variety. Among the six specimens examined by 
myself, one preparation was in peculiarly fine crystals, and gave the 
sp. gr. 2-46 ; two out of the six specimens were prepared by Dr 
