nection made between the latter, and the wheel within the derrick, the driller is ready to commence operations.

Fig. 13.

Fig. 14.

Fig. 15.

There are four principal tools, properly so called, used in the process, viz., the centre bit, the auger stem, the jars, and the sinker bar. In a well that is being drilled these tools hang in the order named, the centre bit being the lowest. This is a bar of iron (Fig. 13) a few feet long with a sharp steel cutting edge on the lower end. To this is attached the auger stem (Fig. 14), which is simply a round bar of 4-inch iron from 28 to 40 feet in length. Then come the jars, two peculiarly constructed pieces of metal so formed that, as indicated by their name, a sudden jar will be imparted to the tools at every upward and downward motion. as the drilling progresses, serving to loosen the bit if by chance it should become wedged in the hard rock. The jars therefore form a very important portion of the drilling tools, being the connecting link between the drill and the means of operating it. Fig. 15 shows them closed, or with the upper wing resting upon the lower one, the improved rounded wing in front concealing the central slot from view, and Fig. 16 shows another pair where both wings are made alike and the links are open. The two sets are precisely alike in principle and vary only in details of construction. The fourth piece, to which is attached a long cable reaching up to the surface, is the sinker-bar (Fig. 17), resembling the auger stem, but only from fourteen to sixteen feet long, and used simply to give additional weight to the other tools.

Figs. 18 and 19 represent sections of the jars shown in Fig. 15.

The cable by which these tools are suspended in the

well passes up to the top of the derrick over the crown pulley previously spoken of, and down again to the bull

Fig. 16.

Fig. 18.

Fig. 19.

Fig. 17.

wheel at the foot of the derrick, around which it is coiled. By applying power to this wheel, the tools may be drawn up from the well and suspended on the derrick, as it is often necessary to do, to get at the bit to sharpen it. The tools are permitted to run back into the well by their own weight, a brake on the bull wheel controlling the motion. About eight or ten feet above the mouth of the well, the cable is fastened to one end of the walking beam oscillating on the samson post, connection being made at the other end of the beam with the engine. By this means a rising and falling motion is imparted to the tools, the impact of the centre bit on the rock drilling the hole. The rate of progress varies of course with the character of the rock. In early times perhaps ten feet a day was considered fair progress, but at present, with tools weighing about one ton and dropping a distance of two feet with every vibration of the walking beam, a very heavy blow is struck and rapid progress is made.

In drilling, the tools are lowered a little with every stroke by means of a temper screw (Fig. 20) manipulated by the driller. With the old-fashioned temper screw a great deal of time was spent in readjustment, for it had to be screwed up thread-by-thread by tedious revolutions of the clamps. But this delay is now obviated. The nut through which the screw passes is cut in halves, one half being attached to the left wing of the screw frame, the other half to the right wing. An elliptical band holding the set screw (Fig. 20 a) passes around the nut. It is riveted securely to one of the halves, and the set screw