161 
remark, that the angles found by careful measurement agree 
with those calculated, as near as could be expected from the 
nature of the case. The angles found in anthracite are 
801% 90% 401% 493 °^ 62% 118% 31% 59% 45% 22i% 
67^% 161% 741 % 52|% and some others; the manner of 
derivation of which, and their mutual relationship, would 
require too much explanation. They are all, however, easily 
shown to be readily derivable from a square prism, which 
has its axes related as 5, 5, and 3, and which is not only 
cleavable with relation to those values of the axes, but also 
to the axes 5 and 5, and four times the axis 3 ; and that it is 
thus cleavable many fragments prove very clearly. I would 
also remark, that careful measurements agree, within a few 
minutes, with the angles calculated on these suppositions. 
Although charcoal is unfavourable for such an examination, 
yet I have found in it angles which agree with those of 
anthracite, as near as could be told. 
Carbon is, therefore, crystallized in three different forms, 
viz., the regular and square prismatic systems, and in hexa- 
gonal prisms : and what is remarkable, (in fact, it is the only 
case of the kind known), it occurs in two perfectly distinct 
conditions, with different volumes, viz., diamond and coke, 
in one system of crystallization, the regular ; making, there- 
fore, four distinct species. 
I will now explain what I believe to be the mutual rela- 
tionships of these four species, and afterwards show in what 
manner their properties differ. 
In order to determine the specific gravity of graphite, 
coke, anthracite, charcoal, and lamp-black, with sufficient 
accuracy, it is necessary to have them in a state of very fine 
powder ; and in the case of charcoal it is absolutely essential 
to boil it first in acid, to dissolve away the glaze of ashes. 
I first heat the powder to dull redness, without access of air, 
and then thoroughly well boil it in water in a bulb of glass, 
