to put in the holes only 4 or 5 ft. apart. The powder must, of course,
be provided with a fuse or preferably a fulminating cap. It is well to
insert the cap at or near the bottom of the cartridge, as shown in
Figs. 8 and 9.

After the charge the usual thing to do is to insert tamping. In the
improved form of hole the tamping should not he put directly upon the
powder, but an air space should be left, as shown at B, Fig. 8. The
best way to tamp, leaving an air space, is first to insert a wad,
which may be of oakum, hay, grass, paper or other similar material.
The tamping should be placed from 6 to 12 in. below the mouth of the
hole. In some kinds of stone a less distance will suffice, and as much
air space as practicable should intervene between the explosive and
the tamping. If several holes are used on a line they should be
connected in series and blasted by electricity. The effect of the
blast is to make a vertical seam connecting the holes, and the entire
mass of rock is sheared several inches or more.

The philosophy of this new method of blasting is simple, though a
matter of some dispute. The following explanation has been given. See
Fig. 10.

[Illustration: Fig. 10]

"The two surfaces, _a_ and _b_, being of equal area, must receive an
equal amount of the force generated by the conversion of the explosive
into gas. These surfaces being smooth and presenting no angle between
the points, A and B, they furnish no starting point for a fracture,
but at these points the lines meet at a sharp angle including between
them a wedge-shaped space. The gas acting equally in all directions