ratchet-bands and cross-head. The latter is held between two check-nuts on the coupling-nut. To this cross-head is attached a bar which communicates with a valve which opens the port when the piston moves back, and shuts it when it moves forward; the air is always on during its backward stroke. The piston having a greater area on the forward than on the backward stroke, overcomes the backward pressure and moves the piston ahead, and when cut off, the continued pressure forces the piston back. This machine is automatic; generally running until some portion of it is destroyed. No part of the machine has been found strong enough to withstand the friction upon it for any considerable portion of time. The union nut has proved its weakest point, and the breaking of this generally destroys that part of the piston to which it is attached. Another point of weakness is the feed ratchet-band, the springs of which are almost continually breaking. The machine consists of eighty pieces; twenty-three of which are screws, fifteen pins, and seven pieces of cast iron. It weighs 240 pounds, runs about 200 strokes per minute, and costs about $400. Its longest run without breaking has been five days. The run of one of them two days without breaking during the time, is considered fortunate. The average breaking is more than one a day. A table showing the list of breakages will follow this description. The piston-head of this machine has a diameter of 4-5/8 inches. The diameter of the piston-rod is 4 inches at the large end and 2-1/4 at the small end. So there are 12-87/100 square inches of air area to drive the drill ahead into the rock, and 4-23/100 to draw it out; but as the air is not taken off from the front end, the actual pressure is upon an area of the difference between the two, or 8-64/100 square inches. Table showing Number of Drilling-Machines Broken, &c. Column Headers A. No. Machines Broken. B. Cross Heads C. Cylinder Flanges. D. Coupling Nuts. E. Feed Springs. F. Feed Palls. G. Ratchet Covers. H. Valve Stems. I. New Packing. J. Tapper Bars. K. Screw Spindles. L. Union Coupling Nuts. M. Feed Nuts. N. Shields. O. Piston Heads.