136 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 1 proposed it to 

 you, I have, within the last week, made seven trials of it, six of 

 v^hich 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. In a cone, the areas of the sections which 

 are parallel to the base, are as the squares of their disrances 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- 

 aholoid ; 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 

 tlie 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, pai'ticular- 

 ly for holes which will receive 

 one as long as eight or ten inches. When tlie workman has formed 

 a just conception of the proper form, he may make one vA\h suffi- 

 cient precision, for any depth of hole, widi no other instrument but 

 a common axe. The pieces, especially when not more than five or 

 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 char2;e in those cases where sand alone may be 



