by the endless screws, f, and the helicoidal wheels, m, is in this way
effected with great regularity. Uprights, a a, of double T-iron, fixed to
joists, k k, and connected and braced by pieces, d d, form a strong
frame.

[Illustration: FIG. 5.--APPLICATION OF GAY'S STONE SAW IN A MARBLE
QUARRY.]

The power necessary to run this kind of saw is less than _n_ × ¼ H.P.,
on account of the number of passive parts. The most interesting
application of the helicoidal saw is in the exploitation of quarries.
Fig. 5 represents a Belgian marble quarry which is being worked by Mr.
Gay's method.

_Tubular Perforators_.--Mr. Gay has rendered his saw completer by the
invention of a tubular perforator for drilling the preliminary well. It
is based upon the same principle as the Leschot rotary drill, but differs
from that in its extremity being simply of tempered steel instead of
being set with black diamonds. A special product, called metallic
agglomerate, is used instead of sand for hastening the work.

[Illustration: FIG. 6.--TUBULAR PERFORATOR.]

The apparatus, Fig. 6, consists of an iron plate cylinder, A, 27½
inches in diameter, and of variable length, according to the depth to be
obtained, and terminating beneath in a steel head, B, of greater
thickness. This cylinder is traversed by a shaft, C, to which it is
keyed, and which passes through the center of the aperture drilled. This
shaft is connected with the cylinder, A, through the intermedium of cross
bars, D, and transmits thereto a rapid rotary motion, which is received