mounted upon a carriage; and for deep rock cutting, mounted upon a tripod. This size will drill from 1 to 40 feet deep and from 2 to 6 inches in diameter.

The 4-inch is for tunneling, heavy straight grading and quarry work, and where 12 to 20 feet holes, 2 to 4 inches in diameter, are to be made in very hard rock.

The 3-inch and the 3-inch are the most used; being found in quarries, railroad tunnels, grading, sewers and mining; the 3-inch drilling a 12 feet hole, 1 to 2 inches in diameter, and the 3-inch drilling an 8-feet hole, 1 to 2 inches in diameter. Below this size there are the 23 and 24-inch drills.

For horizontal drilling the capacities are about less. As regards the capacity of these drills, I annex some figures showing what they will do in various kinds of rock, and in some cases showing the rate of hand work in the same rock.

There is some work, such as cutting slate, granite and marble, where blasting cannot be used for fear of breaking the stone, and in this case 2-inch holes are drilled in a row, two inches apart, and the connection broken down by throwing out the rotation gear, and working out the stone between the holes with a drill bit having a flat point.

As far as possible, the drilling machine should be light, compact, strong, portable, quickly set up and moved, simple in construction, readily repaired at the shaft-head, economical of steam or compressed air, rapid in motion, free from trouble in freezing up where compressed air is used. If possible, the drill should be withdrawn automatically when desired. The machine should strike the blow variably according to the rock being entered. It is desirable that the hole be churned. out by the machine itself, and that the bit shank may be quickly attached to the piston rod. Some like self-feed, some do not. The machine must be readily taken apart and kept clean and in working order. It must drill deep at one setting up. The heads should not knock out, and the tappets, if there be any, should not break. The piston rod should be large.

In the Johnson machine there is self-feed and steam or air pullback. The whole cylinder may be slipped through the body clamp to or from the rock, thus adding to the length of the feed.

In the Bryer drill there are but two working parts-the piston and the rotation bar, the piston being its own valve, regulating the admis

Place or works.

sion, cut-off and exhausts by annular grooves in the cylinder and piston. It is steam-cushioned at each end.

In the Rand drill the tappets are moved by the piston instead of by projections upon the piston rod. The feed in the machine is by hand, a square-threaded screw carrying the cylinder along on its bed-plate, which latter has a vertical pivot.

In the Burleigh tappet drill there is a trough with ways on each side, in which the cylinder slides. The screw feed is automatic. The piston rod, which has a double annular cam and spiral grooves, controls the valve, effects the feed, and causes bit rotation. It is sometimes mounted in gangs in a frame or carriage, two on a horizontal bar across the top and two at the bottom, each having adjustability in these planes.

The single drill is mounted on a threaded telescopic iron column, having a single sharp point at the bottom and an iron thrust claw at the top. This column may also be used horizontally for shaft work.

The new Sergeant drill, made by the Ingersoll Rock Drill Co., was described at length, and illustrated, by Mr. F. L. Miller, in a paper before the Engineers' Club of Philadelphia, September, 1880. I show upon the screen the working drawings of the latest form. The principal peculiarities are in the valve and the ports and passages. The valve is a cylinder, having flanges somewhat smaller than the cylindrical steam chest, in which the valve slides upon a central bolt, which serves to hold the chest heads together. The chest heads have rubber cushions. The piston is of great length, and has a cavity as long as the piston stroke, so that it will always register with the ports and allow the steam exhaust from the valve to be exhausted therein. We will suppose the valve at one end of the stroke and steam let into the chest; the steam will pass to the cavity between the flanges, the steam being exhausted at the other end there will be no opposition to the valve moving towards that end, by reason of the steam rushing past the flange nearest the valve cylinder end. The cavity in the main piston prevents the valve being shifted until the main piston is nearly at the end of its stroke, when it will uncover the exhaust port of the valve cylinder in which the steam is confined, the steam passing into the upper port then to the opposite end of the chest, then by the lower port to the cavity in the piston. Rotation is by a fluted bar and nut; and feed by hand.

RADIO-DYNAMICS.

By PLINY EARLE CHASE, LL.D.

Abstract of lectures delivered before the Franklin Institute, March 10 and 17, 1881.

Your committee have invited me to lecture upon some of the results of investigations in which I have been specially engaged. My subject is given, in one part of the announcement, as astronomy; in another, as the music of the spheres. The former title is so far appropriate as it designates the source from which the greater part of my discoveries have been derived; the latter, as indicating the universal harmonies which are manifested, both by atoms and by stars, by microscopic and macrocosmic spheres alike, and which are, as I shall try to show you, the necessary results of the plan which has established the stability of the physical universe.

It will be impossible, in two lectures, to do more than glance at a few of the instances of prevailing rhythm, but I think you will find those which I have time to bring before you quite sufficient to serve as the solid groundwork of a science which is both the oldest and the newest of all sciences-the science of photo-dynamics or radio-dynamics. I call it the oldest, because we are told in Genesis that the first act of the Creator, in educing order out of chaos, was the command: "Let there be light;" the newest, because its right to recognition is as yet but sparingly and somewhat hesitatingly accepted, and because nearly all the materials, with which it has to deal in its systematic coordination, have been collected within the last quarter of a century.

The scientific spirit strives always to ascend from the special to the general; from multiplicity to unity. The Greek philosophers looked, in turns, to each of their four elements-earth, air, fire and wateras the basis of all things. Newton, in his "Principia," demonstrated many propositions which are applicable in all fields of physical investigation, but he used them only for explaining the motions of the various members of the solar system. He spoke, however, of an "æthereal spirit," as a possible medium in universal gravitation, but without giving any hint of believing that any of its properties were within the reach of physical research. Franklin's experiments in

electricity furnished a foundation for electro-dynamics, and led to a

belief, which is still widely held, that in the various forms of electrical manifestation the clue to all physical activity is to be found. Mayer, Joule and their collaborators opened the gates of that fairyland of science which Tyndall has so admirably described in his "Heat as a Mode of Motion," and there are many who now believe that all material phenomena are susceptible of an explanation by thermo-dynamic laws.

The theory of the "correlation of forces," which teaches that light, heat, electricity, magnetism and chemical affinity are all forms of a single energy, and that they all may be interchangeably converted, provided the proper conditions are observed, may be thought to imply that neither of the correlated sciences is entitled to any precedence over the others, but that each of them becomes tributary to the general science of universal physics, so far as it develops laws which are of universal application.

Sir John Herschel appears to have been the first investigator who ever proposed any numerical estimate of the energy of light. It is a well-known proposition that the velocity of wave propagation, in elastic media, varies directly as the square root of the elasticity and inversely as the square root of the density. He accordingly stated, in his "Familiar Lectures on Scientific Subjects" (pp. 281-3), that the elastic force of the air, in its resistance to compression, would require to be increased "in proportion to the inertia of its molecules" more than 1,000,000,000,000-fold, to admit of the propagation of a wave with the velocity of light, and that this enormous physical force is perpetually exerted at every point through all the immensity of space. He also said (p. 218): "It must be remembered that it is Light, and the free communication of it from the remotest region of the universe, which alone can give and does give us the assurance of a uniform and all-pervading energy."

In the eloquent extract which is quoted by Tyndall (op. cit., 4th ed., section 707), Herschel had previously stated that "the sun's rays are the ultimate source of almost every motion which takes place on the surface of the earth." Tyndall, with equal eloquence (Ibid., section 724), describes the flux of power which "rolls in music through the ages," and shows that all "the integrated energies of our world are generated by a portion of the sun's energy which

does not amount to 2300000006 of the whole."

These extracts seem to furnish a sufficient reason for looking upon