ve ee Blasting of Rocks—Danger and Remedies. 
it with coarse dry sand. If the hole be very shallow, the sand may 
be pressed down around the cone with a small wooden rod, but if 
the length of the cone be eight or ten inches this will be unnecessary. 
For the purpose of testing this method, before I proposed it to 
you, I have, within the last week, made seven trials of it, six of 
which were successful. The failure of the other, I attributed to the 
circumstance that the cone was so large at the base as to bind on the 
sides of the hole. The same hole was afterward charged, using a 
smaller one, and the blast was effectual. 
I have spoken of the piece of wood to be used in this method of 
blasting as a cone. Strictly speaking, however, its form should not 
be that of a true cone. Ina cone, the areas of the sections which 
are parallel to the base, are as the squares of their distances from 
the vertex ; but the proper form for the pieces of wood, is that in 
which these areas are not in the duplicate, but in the simple ratio of 
the distances from the vertex. This gives the form of the true par- 
aboloid ; and to this form the workman, in making the piece, should 
certainly approximate as nearly as convenient ; particularly as it res- 
pects the main part of the length, from the base toward the vertex. 
Near the vertex the form will not be so important. It is more con- 
veniently formed, and is perhaps better, to terminate in a conical point, 
rather than in the more obtuse form of the paraboloid. 
I here give a longitudinal section, showing on a small scale, nearly 
the form of the pieces which I used in my experiments. 
It will be proper to remark 
here, that no very great degree 
of precision will be necessary 
in forming the pieces, particular- 
ly for holes which will receive 
one as long as eight or teninches. When the workman has formed 
a just conception of the proper form, he may make one with sufli- 
cient precision, for any depth of hole, with no other instrument but 
a common axe. The pieces, especially when not more than five oF 
six inches long, should be made of hard seasoned wood. When once 
made they may sometimes be used several times in succession, aS 
they will not often be thrown to a great distance ; sometimes not even 
out of the hole. In my experiments I used one piece three times 
and another twice. 
Though the time occupied in charging in this way, is somewhat 
‘more than it takes to charge in those cases where sand alone may be 
