159 
attendant on blasting ; the use of firemen understanding 
and observing the barometer; the error of supposing the 
wastes to fill up rapidly and entirely by subsidence; and, 
most of all, the hopelessness of increasing the speed of 
the air current, where candles are used, much beyond its 
present rate ; — these are among the considerations which 
either have not occurred to those reporters, or have im- 
pressed me more strongly than they appear to have done 
these writers. 
I end as I began ; all that I have here collected and 
compared, all besides that I have read, all that I hear, 
even from those who advocate reliance on some single 
means of defence, convinces me that a single means is not 
enough. It will not do to trust alone to a strong current 
of air, to the superiority of " long" methods of working 
over " short," or " short" over " long," to the use of 
lamps, to frequent and minute inspection, or to regulations 
for workmen. Let each, or any, be observed ; but let no 
other helps to safety, which are applicable to the situation 
and circumstances be neglected. 
ON THE EXISTENCE OF FOUR CRYSTALLINE SPECIES OF 
CARBON. BY H. C SORBY, ESQ., F.G.S. 
The four species of carbon are diamond, graphite, hard 
coke, and charcoal. They have long been distinguished 
practically ; and the object of the present paper is to show 
their various crystalline forms and mutual relationship. 
In the first place we have diamond, which is well known 
to be crystallized in the regular system, and to have a spe- 
cific gravity of about 3.52. 
Secondly, we have graphite or plumbago, which is found 
crystallized in regular hexagonal prisms, and has a specific 
gravity of about 2.18. 
VOL. III. l 2 
