46. I will now offer a few remarks with respect to the construction of
the _Double Triangle Wheel_. This piece may be made by employing two
hexagonal frames of wood of the same size, in a centre twice as long as
that described in fig. 60. But it may also be made in such a framework
as Mr. Darby will supply, which is a nave made of light wood, with six
spokes, cut at their ends in such a manner as will allow the cases to be
firmly attached. But whether you use the one form or the other, the
principle is precisely the same, and the cases must be arranged as shown
in the adjoining diagram (fig. 65).
[Illustration:
Fig. 65.
]
The performance of this wheel is, of course, the same as that of the
single triangle wheel, and differs from it only in the matter of
duration. But it must be borne in mind that a double triangle wheel,
having six cases upon it, would be a very slow sample of pyrotechnic
beauty _if all these cases were filled with the same composition_. It
would, indeed, be a most meaningless performance. You must therefore
take care that some variation is made, using at least two varieties of
composition. You will then have an effective piece, capable of lasting a
long time in proportion to its size.