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_ x 1/4 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, 271/2
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
at the upper part from a telodynamic wire that passes through the channel
of the horizontal pulley, P. This latter is supported by a frame
consisting of three uprights, Q Q, strengthened by stays, R R, fixed to
the ground.

In order that the cylinder, A, may be given a vertical motion, cords, M
M, fixed to a piece, S, loose on the hub, D, wind round the drum of a
windlass, T, after passing over the pulleys, p p.

The rapid gyratory motion of the cylinder, along with the erosive action
of the metallic agglomerate, rapidly wears away the rock, and causes the
descent of the perforator. During this operation a core of marble forms
in the cylinder. This is detached by lateral pressure, and is capable of
being utilized. The tool descends at the rate of from 20 to 24 inches per
hour, or from 8 to 10 yards per day in ordinary lime rock.--_Le Genie
Civil_.

* * * * *

PORTABLE PROSPECTING DRILL.

[Illustration: PORTABLE PROSPECTING DRILL.]

The Aqueous Works and Diamond Rock-boring Company, Limited, of London,
s