A third machine, called the Burleigh drill, an improvement upon the preceding one, was next produced, which is now at the works on the East Heading. About $13,000 was spent upon these experiments, resulting in the construction of the Brooks, Burleigh and Gates drill, and the manufacture of four of them. About one-half of this expenditure may be charged to these last drills; the other was unproductive of anything of value. The Brooks, Burleigh and Gates drill was patented, but the Commonwealth has the right to use them in the construction of the tunnel. These machines will now be described. THE HANSON MACHINE. This machine has a cylinder and valve motion, similar to a steam-engine. The piston is hollow, the drill-bar which may be of any required length, passing through it, is moved with the piston, by means of four wedges or cams on each end of the piston; these cams are pressed on the drill-bar by means of sliding collars forced upon them by a complex arrangement operating alternately. The drill-bar is rotated by means of a ratchet operated by a spiral groove in the shield of the machine. The main difficulty in this machine was in the complex arrangement for forcing the collars upon the cams or wedges. It did not work well in a horizontal position. The machine consisted of one hundred and twenty pieces, and weighed five hundred and ninety-five pounds. THE BROOKS, BURLEIGH AND GATES MACHINE. This machine has a hollow piston, the drill-holder being a screw passing through the piston, moving with it, and fed through it, by means of a nut on the end of the piston-rod. This nut is held by means of a cap or union nut, as it is called, the union nut being screwed on to the coupling, and the coupling nut screwed to the piston-rod. The feed-nut protrudes through the union nut, and is allowed to turn round in it. On the end of this feed-nut is a ratchet gear covered by a ratchet-band with an arm upon it, all moving with the piston. The ratchet arm moves up and down in a spiral groove, the groove being in a shield attached by screws to the cylinder; on the ratchet-band there is a pall and two springs, one under the other. One of the springs holds the pall in gear, the other holds it out of gear. As the piston moves down, the outer spring comes in contact with a trip which is on the shield and is lifted up, allowing the under spring to throw the pall into the ratchet, and as the piston is moved back, turns the nut round, thereby feeding the screw forward. At the extremity of its backward stroke, the pall comes in contact with another trip on the shield which lifts it out of gear, the outer spring having a catch upon it which holds the pall when thus lifted out. The rotary motion is given by a ratchet on the coupling-nut, covered by a ratchet-band the arm of which moves in a spiral groove in the shield similar to the other, only having a spring to hold the pall in the ratchet; this rotates all the parts on the piston except the