Sandy Hook, Mantoloking and Cape May, N. J.; Cape Henlopen and Bethany Beach, Del.; Hog Island, Smith Island and Cape Henry, Va.; Cape Hatteras, Cape Lookout, Cape Fear, North Island, Bull Island and Morris Island, S. C.; St. Augustine and Key West, Fla. The gulf stations are at Burrwood, Pass a Loutre and Grand Island, La.-Naval Monthly, May.

The recent developments of wireless telegraphy have required the use of more powerful Hertzian waves than had been sent out by any station up to the time of the war. There are present, therefore, in the ether permeating and surrounding the atmosphere, numerous trains of waves traveling in all directions. It is altogether possible that one of these sets or a set resulting from a combination of several of them should come in contact with a number of conducting bodies so arranged in a casual manner as to form a Hertzian resonator of the required inductance, capacity and resistance to respond to the passing train. There would then be an ether wave excited in the system, a spark would be produced and a fire probably caused as the result of the passage of the wave.

Mr. George A. Le Roy has presented to the Académie des Sciences a note on the possibilities of a fire being produced in this manner. He conducted a laboratory investigation by means of an apparatus which he terms "inflammatory-resonator." It consists of a globular glass flask provided with four openings, two lateral, one at the top and one at the bottom. Through the lateral openings two electrodes are introduced and kept at the desired distance apart by an adjusting mechanism; they constitute the terminals of a Hertzian resonator. The bottom opening permits placing under the electrodes a plate which carries the inflammable substances; there is also at the bottom a connection for exhausting air with a pump, or introducing gases into the globe. Through the top are located the required measuring instruments.

Hertzian waves of relatively low intensity, generated by means of an ordinary Ruhmkorff coil, were sent through the instrument.

Mr. Le Roy asserts that iron electrodes facilitated the inflammation of cotton, amadou, paper, tow, etc. He, therefore, concludes that a condition may be produced in such a case as the piling of a number of cotton bales, when by the breaking of one of the iron bracings an open resonator is virtually formed.-Mechanical Engineering, May.

ENGINEERING

MEANS FOR INCREASING POWER OUTPUT OF AIRCRAFT ENGINES AT HIGH ALTITUDES.-Maintaining Constant Pressure Between the Carburetors of Air Engines Regardless of the Altitude.-Leslie V. Spencer. It is well known that at high altitudes the power developed by the ordinary internalcombustion engine decreases materially because of the decrease of the oxygen content in the cylinder charge. The Bureau of Standards curve between the pressure and altitude at a temperature of 50° F. illustrates this fact very well. From it, it appears that at 20,000 feet an engine operates with an intake pressure of approximately half that at ground level, which affects both the proportion of the mixture and the fuel delivery through the nozzle.

In order to overcome this difficulty in the operation, engineers have turned to the idea of supercompressing the air sent to the carburetor so as to maintain as nearly as possible the ground-level pressure regardless of the height. Such supercompression has been given various names, of which the present writer recommends the term supercharging." The function of a supercharging device is, however, not to increase the normal ground-level power up to the limit in altitude for which the supercharger is designed.

In Europe the method apparently most widely used is the turbo-supercompression, a good example of which is represented by the Rateau scheme developed by Professor Rateau in France.

The rotary compressor has been tried in competition with the centrifugal type of compressor by the British at the Royal Aircraft Establishment and has been discarded in favor of the latter. The centrifugal form of compressor, however, has proved the most desirable through having a minimum of working parts, being very compact for a given capacity and being capable of operating satisfactorily at top speed over long periods of time.

30 28 26 24 22 20 18 16 14 12 10

Barometric Pressure, Inches of Mercury.

Bureau of Standards Curve between Pressure and Altitude at Temperature

of 50° F.

As to the methods of driving the compressor, there are three possibilities. It can be direct-connected with the engine just as a magneto, possibly with a gear train to step up the speed of the compressor rotor.

Also the compressor might be driven by a small steam turbine, the steam being produced by the exhaust-gas heat. The third alternative is to drive the compressor impeller by means of an exhaust-gas turbine receiving its energy directly from the engine exhaust gas.

In England and Italy direct-connected means of drive through an intermediate gear train have been tried, but great difficulty was experienced in coping with the severe stresses developed in the rapidly operating mechanism due to sudden fluctuations in the speed of the engine.

Steam-turbine drive has not been seriously considered because of the obvious complications and it is the exhaust-gas drive that has found the best favor. The exhaust-gas turbine can be connected directly with the exhaust ports of the engine through special manifolds replacing the standard manifolds, so that all the exhaust must pass through the turbine nozzles and give up its energy to the turbine rotor before being allowed to escape into the atmosphere through the turbine discharge passages.

In the designs which have been experimented with thus far, the turbine rotor and the impeller of the centrifugal compressor are mounted on the same shaft so that the two are in one unit.

The only difficulty that has been encountered is that of coping with the high temperatures of the exhaust gases, but even this difficulty seems to be close to satisfactory solution.

Around the turbine rotor there is atmospheric pressure while the supercharged engine exhausts at a normal pressure of about 30 inches of mercury corresponding to a normal atmospheric pressure of 15 pounds per square inch at sea level. The expansion of the gases from this pressure to that of the atmosphere is sufficient to operate the turbine at high speeds, and ordinarily the turbine rotor speeds run up to 25,000 or 30,000 r. p. m.

Experiments with this system indicate that of the energy of combustion the engine and turbo-compressor utilize about 33 per cent, whereas approximately 45 per cent is lost in the exhaust which finally escapes from the discharge ports of the turbine.

In addition to the work of Professor Rateau and other foreign experimenters a certain amount has been done in America, where at the request of the government, E. H. Sherbondy and Dr. Sanford A. Moss, Mem. Am. Soc. M. E., have taken up the same problem.-Aerial Age Weekly, vol. 9, no. 5, April 14, 1919.

AERONAUTICS

PULLING THE TRIGGER BY FLUID PRESSURE.-The German has been shown up by the late war as an imitator rather than an inventor. The Germans took over and improved the submarine and the machine-gun and a host of other British and French and American inventions; but there was one little invention, which first saw the light during the war, and which Fritzie never was able to use-apparently for no other reason than the very good one that he couldn't figure out how it worked. This was a device, weighing but a few pounds, known to the initiated as the "C. C. Gear." It was this gear which gave to the Allies a goodly portion of their indisputable mastery of the air, and was thus instrumental in bringing the war to a more speedy close.

This device is far from being a complicated one. It contains no intricate mechanism, operating merely by pressing a button or lever. Yet it successfully defied solution by every noted scientist of Germany and Austria for a period of two years during which samples of it were continually falling into Boche hands on captured planes.

The term gear" as used by pilots of the air signifies a mechanical device by means of which a machine-gun may be timed to fire between the fast revolving blades of a propeller. There are more than a few of such devices; the one most used at the time when the idea first gained acceptance was illustrated in these columns a couple of years ago; but the C. C. gear differs from all the rest in the fact that it is non-mechanical. The tremendous advantage of this will be realized when it is remembered that the terrific speed at which it must operate necessitates the timing of the gear to fire accurately 700 shots a minute through a two- or fourbladed propeller revolving 2000 times a minute.

The history of the gear is romantic in the extreme. When the war started in 1914 no one beyond the novelists of perfervid imagination had any idea that aerial combat would develop to any great extent. The first pilots were chivalrous fellows. A Hun flier darting past a British or French machine would wave his hand genially, and receive a cheery salutation in return. Airplanes were solely for reconnaissance purposes.

Then, one day, a Hun, with villainous intent, pulled out a revolver and took a pot shot at a Britisher. The Englishman was surprised; he hadn't

thought of that. From that time the war in the air was on; revolver duels became common enough. No one was ever hit, but it was good sport. Even when a British pilot endeavored to make the game a bit more exciting by taking a shotgun aloft with him, and when the Huns retaliated, these weapons were found to be little more dangerous than their predecessors-though it is on record that one enemy machine was thus brought

down.

Eventually a pilot, more daring than the rest, conceived the idea of using a machine gun. The Lewis, being light and exceedingly mobile, was the first choice. It was a great improvement, and all parties concerned

recognized it as such from the first. Planes began to carry machine guns as a matter of course; and the only drawback was the limited area in which the gun could be fired-only at right angles to the direction in which the machine was flying, in the majority of instances.

One day a pilot took a chance and fired straight ahead through the propeller. It was a risky proposition; but on landing it was found that comparatively few of the shots had hit the blade—about 4 per cent to be exact. It was, however, expensive as well as dangerous, with propellers costing $100 and more. So the next step was to armor-plate the blades so that the bullets would glance off. But this threatened to put a stop to formation flying, because the bullets, ricocheting in all directions, were as much of a menace to friend as to foe.

One summer afternoon, three years ago or thereabouts, a flight commander on the western front was surprised to hear a Hun plane overhead rattling off bursts of 40 or 50 shots with surprising ease. A pilot was sent up to bring the stranger in, and by great good luck he succeeded. When the Hun was shot down it was discovered that a novel contrivance of rods and levers had been fitted to the engine synchronizing the firing of the gun with the revolutions of the propeller, thereby making it altogether safe to fire through the rotating blades. It was at best a crude contrivance, but a vast improvement over indiscriminate fire.

This gear was turned over to a naval lieutenant who made a number of improvements, the finished product being known as the Scarff gear. The idea once in hand, numerous mechanical gears were brought out, but all were handicapped by one great drawback which it seemed impossible to overcome. The timing was a delicate operation, and the adjustments necessarily fine. The mechanical gear, constructed of metal parts, could be timed perfectly on the ground, but the intense cold of the higher altitudes caused the metal to contract, and the timing would be thrown out of adjustment. Furthermore, the very active friction of the working parts caused severe wear, and so tended to nullify the accuracy of operation.

The problem came to the attention of M. Constantinesco, a Rumanian by birth, naturalized in England, and he applied to it a principle in which he had just become greatly interested—namely, the transmission of power through a column of fluid. Because he encountered this principle while experimenting with sound waves under water, he named it the "sonic" principle. He emphasizes that it is not as though the fluid were a rigid column, and imparted shock in the same way that a sledge imparts the blow of a hammer to a bar upon which it is held by a second workman. There is actually generated, by an impact upon one end of the column, pressure wave, which traverses the column at the rate of 4900 feet per second, delivering a blow at the other end, not instantaneously, but after the lapse of the infinitesimal interval called for by this velocity and the length of the tube. It was doubtless their failure to appreciate that the outfit did not constitute a rigid system that kept the Germans from learning how to operate it-for its advantages are so marked that had they been able to unravel the secret, they would surely have used it.

M. Constantinesco's apparatus consists essentially, as our drawing shows, of a copper pipe filled with oil, at one end of which is a piston and at the other a pushrod to operate the trigger. The piston is connected with the propeller shaft by a gear and a cam. At the proper instant in each rotation of the propeller, the hump on the cam drives the piston down upon the end of the oil column, which is under a pressure of 150 pounds. Through this compressed column the shock of the piston blow travels as a pressure wave; and when it reaches the other end it operates the firing mechanism. The rotation of the propeller generates 40 to 60 of these wave impulses per second, with no friction except the very slight amount to be found between the gear and the cam.