charge; and the deck of a vessel presents, by far, the greater portion of the target subject to fire. Again, granting that failure to perforate the heavier armor may ensue, yet the concussion and shock will doubtless be felt in the disarrangement of the machinery and breaking of weaker parts some distance from the point of impact, not to speak of the physical effects of the enormous shock upon the crew in the vicinity. Failing to strike the ship, the dynamite shells are now arranged so as to explode after they are entirely submerged in the water. Here an explosion anywhere within twenty-one feet would be fatal according to Gen. Abbot's formula.

This adds a very large area of vulnerable parts to that of the already large area of the deck. Even if exploded at a greater distance than twenty-one feet, up to about thirty-five feet, the effect would probably be injurious to the propelling machinery, and practically paralyze the ship.

In order to safely propel charges of the high explosives against the submerged portions of an enemy's ship, a number of complicated and expensive propelling-torpedoes have been devised. The one most generally used is the Whitehead fish-torpedo. It has a maximum range of eight hundred yards, while two hundred yards is the greatest distance for certainty of action. Its speed is twenty-seven knots per hour.

The extreme range of the Lay torpedo is two miles, and the mean speed about twenty knots. It is steered and fired by means of a connecting cable.

The Sim's electrical fish-torpedo is propelled by electricity from a dynamo on shore or on shipboard, and is steered from there. This is entirely submerged and kept at the desired depth by means of a float which maintains its buoyancy even after it has been repeatedly perforated. But, on account of having to drag this large float, the speed is very slow. The largest one yet constructed has a range of two miles, with a speed of about eleven knots. This, as well as the Lay torpedo, has to be seen throughout its course to strike the enemy, which is a matter of no little difficulty when the water is rough. All the moveable torpedoes have the common disadvantage that they can be stopped by netting properly placed, and if expended without effect, a considerable plant has been lost.

The torpedo shells projected by the pneumatic torpedo-gun can

attain a range of two miles in twenty-two seconds, and they can be directed against the enemy much more accurately than appears possible with the others. If it misses the target, the only expenditure is the shell and its charge. Placed, for defence of harbors, within fortifications, they can be brought into use at a time when the enemy's fleet comes to close quarters,- that is, within two miles, the present effective range of the gun. They could be placed on board swiftmoving torpedo-boats, which could approach a beleaguering fleet, at dusk or at night, within a mile, and deliver a most damaging fire. Where the enemy has succeeded in removing existing torpedo-obstructions, these machines can shower its pathway with torpedoes which, when the depth is suitable-say fifty to sixty feet or less-can be arranged to explode either directly upon reaching the bottom or at any desired interval. On the other hand, in making an attack in a port, torpedo-boats, armed with the pneumatic gun, could strew the channel, through which the fleet is to advance, with the torpedo-shells, arranged to explode, some, soon after reaching the bottom; others, when fully submerged. These, if dropped at short intervals, would inevitably break up any system of torpedoes which can be planted.

In warding off the attack on a ship by any of the movable torpedoes, if they should be discovered approaching, I can think of nothing which has so many chances of success as the torpedo-shell projected from the pneumatic gun.

A vote of thanks to the speaker brought the meeting to a close.

MEETING 341.

Late Methods of Drilling for Oil and Natural Gas.

By MR. F. H. NEWELL.

The 341st meeting of the SoCIETY OF ARTS was held at the Institute on Thursday, January 7th, at 8 P. M., Prof. L. M. Norton in the chair.

After the reading of the minutes of the previous meeting, the chairman introduced Mr. F. H. Newell, who read a paper on "Late Methods of Drilling for Oil and Natual Gas."

Mr. NEWELL said: The problem which the would-be producer of crude oil, or natural gas, has before him is something like this: At an average depth of about fifteen hundred feet there probably is a stratum of sandstone, which, though quite compact and well cemented, holds in the interstices, between its grains, oil or gas, probably existing as a fluid, under enormous pressure.

To reach this store of oil he must penetrate, first, the surface soils and drifts, which vary in depth from a few inches on the hills to four hundred and fifty feet in the valleys; then, below these unconsolidated deposits, the more or less firm strata of the coal measures, or upper Devonian, lying horizontally, and consisting mainly of shale with beds of sandstone and occasionally conglomerate interstratified in every variation of order and thickness. The surface deposits of gravel and clays are saturated with fresh water, as is also, as a rule, the consolidated rock near the surface. Below the fresh-water bearing strata are found, occasionally, layers full of salt water, and usually below these the shales, even for a thickness of a thousand feet, are completely dry until the oil-bearing sondstone is reached.

It is probable that the permeability of the oil-bearing sandstone, and therefore its ability to deliver oil into the well, is injured by these surface waters entering the sandstone, and the pressure of this fluid, standing in the well, interferes with the free movement of oil towards the hole. Therefore, the completion of an oil or gas well requires the successful performance of at least three operations: making the wellhole through soil and rock, preserving its shape by pipe through unconsolidated gravels and soft rocks, and the exclusion of water.

There have been suggested several ways of sinking wells: first, the one in use since time immemorial, i. e., digging. This method has actually been tried; oil-shafts have been sunk, not only in the Old World but in the oil-fields of Pennsylvania and Ohio; and it is a significant fact that of these shafts none, as yet reported, have yielded a larger amount of oil per day than the small drill-hole made in advance, though the drill-holes were only five inches in diameter, and the shafts at least five feet, thus exposing at least twelve times as much wall surface. Hence economy dictates that the well should be made as small as possible. To do this a diamond-drill might be used, but as a fact, this machine, though so useful in inclined strata, or where it is desired to bore in other directions than the vertical, or

where exact samples of the rocks passed through are of first importance, cannot compete in cost with the cruder methods in present use. The method in almost universal use is drilling by walking-beam and rope, but it must be remembered that this way of drilling is only applicable in comparatively soft rocks, such as limestones, shales, sandstones, and moderately well-cemented conglomerates, where they are horizontally bedded and unfissured, for the drill, guided largely by its own weight, is easily deflected by inclined bedding, cracks, or planes of weakness, and, once turned from the exact vertical, soon binds and refuses to work, and the hole is straightened only after considerable delay and expense. The art of drilling has grown, by the inventions and discoveries by hundreds of men, from one very simple operation to a business using in special cases an almost innumerable variety of tools, and having large establishments to make its peculiar machinery.

The growth of this specialized industry of making drilling-tools has been accompanied by the adoption of certain standards of sizes of tools and machinery, as also of hole and material inserted, so that at the present time and for some years past all wells are, and have been, drilled of the same size.

Some of the principal considerations which governed the choice of a certain diameter of well are: the smaller the hole the less iron is used in casing; also less material must be removed, thus faster time can be made, the same weight of tools being used. But, on the other hand, the smaller the hole the longer the drill must be to give the necessary weight. It eventually becomes too long for strength or convenience in handling, and, as a compromise between these, the diameter of five and a half inches has been adopted, so that now there are probably over twelve thousand wells of this diameter, ranging in depth from six hundred to two thousand feet.

The principle of ordinary drilling is very simple, the operation being but the employment of machinery to lift and let fall a heavy drill. The drill is suspended from a rope attached to the end of an oscillating walking-beam, at each stroke being turned, so that it may cut a round hole.

When the fine sand and mud, made by the constant pounding of the rock, has accumulated so as to interfere with rapid cutting, the drill is taken out, water is poured into the hole, if not already there,

so as to form a very fluid mud, which then can be bailed or pumped out. The drill is then put back, the operations of drilling and pumping being alternated for every five feet of advance.

The drill is composed of several parts, viz., the bit, stem, jars, sinker-bar, and rope-socket, screwed together with tapering steel joints, and weighing in all about twenty-two hundred pounds. The bit is three and one half feet long, and weighs about one hundred and forty pounds. Its steel point is dressed to an obtuse cutting-edge to fit into a circular guage five and five-eighths inches in diameter, so as to insure its cutting a round hole. Bits were formerly made tapering, and dressed like a cold-chisel, a circular reamer being used at intervals to true the hole. The stem is three and a half inches in diameter, and usually thirty-two feet long, but sometimes fifty feet long. It weighs about twelve hundred pounds.

The jars consist of two interlocking slotted pieces, having a longitudinal play of nine inches. When the bit is stuck the top piece slides down, and then is pulled up, giving a sharp upward blow, rapidly repeated, thus loosening the bit, when it could not have been started by a direct pull on the cable.

The sinker-bar is twelve feet long, and weighs four hundred pounds. Its use is to give greater efficiency to the blow in loosening the bit. The cable on which the drill is hung extends up above the surface of the ground, and is held while drilling by clamps, which can be lowered as the drill advances by a device called the "temperscrew," suspended from the end of the walking-beam. The bailer is four inches in diameter, and about twenty feet long, made of thin galvanized iron, with a cone valve in the bottom.

The wood-work and moving parts making up the machinery for handling the tools is included in the term "rig," of which the most important object is the derrick. This is seventy-two feet high, twenty feet square at the base, and three feet square at the top. Its object is to carry a pulley to a sufficient hight to swing the tools when taken out of the hole. It is built of two-inch plank, cross-braced by boards. The heavy foundation-timbers of derrick and machinery are all gained and keyed together, so that all parts can be quickly lined up or tightened. No masonry is used in any part.

In beginning a well in the valleys where the loose earth is of great thickness, the important and expensive operation of keeping this