soldiers are crowded into taxicabs and shifted in an incredibly short time. Automobiles are constantly dashing about in the rear of the battle lines. General Joffre, the commander of the forces of the Allies in France, uses racing machines of the highest power, and can go from one end of the battle line to the other in less than four hours, for he travels at sixty miles an hour. No staff officer goes anywhere on a horse. He uses an automobile.

More than that, the Germans and presumably the French, have taken auto delivery trucks of the heavier type and mounted field guns on them. These can be moved in any direction almost instantly. They constitute the most mobile artillery the world has ever known. In other wars artillery was shifted by horse or by hand. In this war some of the lighter guns are automobile guns, and they can be transferred from one point to another while horses are being brought up.

The Belgians have built many barbedwire entanglements, and so have the French; but gasoline makes these seem like paper obstructions. The Germans have heavily armored automobiles with great knives in front and steel frames running back over the tops of the cars. With these tremendous clippers they charge full tilt at the barbed-wire obstructions and dash through them. The knives on the fronts of the cars cut the wires and the steel frames protect the men operating the cars. Also, there are armored automobiles that dash about the country carrying riflemen, and light rapid fire guns that do their share of execution. Automobile trucks bring up the ammunition.

It is in the commissariat, however, that the automobiles are most useful. They prove that the army travels on its gasoline. Great trucks bring supplies of food to certain bases. Light automobiles take loads of this food, and distribute it along the line, scooting back and forth, from base to given. point of deposit and back again, making quick trip after quick trip, and covering the distances and doing feats of delivery that would be impossible for horses. Thus, too, by means of the smaller autos the men at the front are in constant and rapid communication with all points in the rear. The mobility of these great

armies has been doubled and probably tripled by the gasoline engine.

The German system is evidently the result of long preparation. The Germans were ready. When their army is moving there is a constant procession of small automobiles-or comparatively small ones-running back and forth between front and rear, in certain welldefined lanes, bringing up whatever may be needed from the big trucks that labor behind but move far faster than any teams of horses could. The Germans use automobiles for every possible contingency save the shifting of their great siege guns. These are so big and so heavy that they are driven by thirty horses.

English soldiers returning wounded from the front, or straggling in, report familiar busses in all parts of France.

A friend of mine who was in a certain part of France told me he met on a French road the very omnibus he had constantly used in going from his office to his home, clattering along, loaded with supplies, and making as good time as it did on the asphalt of London. Big vans and trucks with the familiar names of London firms on them are continually popping past the British soldiers in France and being cheered. Busses that for years took peaceful Londoners, and peaceful Manchesterians and peaceful people of Liverpool and of other cities, about their towns on business or pleasure now bring wounded soldiers back, or bring up ammunition or food. The smell of petrol along a battle line is as strong as it used to be on the Strand on a foggy day.

It is not only for trucking or for transportation purposes that gasoline is indispensible. Gasoline is the motive power for the engines of the aeroplanes. As warfare is now conducted the flying corps of each army is one of the most useful arms of the service, if not the most useful. The airmen perform prodigies of valor in scouting, in determining locations, in finding ranges, and in plotting out the lay of land. It is a good example of the repression of the British War Office that none of the English papers printed a word about the flight of the English aeroplanes to France.

That was the most inspiring sight of this war. Fully thirty of them-per

haps more rose one day and flew, like a great flock of white-winged birds, straight across the Channel and landed without a mishap. Since that time these aeroplanes have been hovering over the lines of the enemy, finding ranges for the artillery, and doing many other hazardous things. The French have a great number of them and so have the Germans. The aeroplane as a factor in war is as common as the automobile.

Shooting Into the Air.

The greatest value of aeroplanes is in finding ranges. In these days, in the formal engagements, the riflemen ' and the artilleries shoot at marks they cannot see. A man shooting from the ground can see about fifteen hundred yards. Frequently he is shooting at an enemy two thousand yards away. The artillery is behind the rifles. So the airship flies straight over the enemy's line, determines the range, flies back and communicates it to the artilleries. Then, with the range determined, the artilleries can land their shells at any given point with the utmost precision.

The bomb-dropping feature of airships of whatever sort is rather futile. Though an airship can find a range for a gun, it cannot apparantly drop a bomb with any precision from any considerable height. Such bombs as have been dropped have evidently been dropped in the hope that they might hit something, rather than in the expectation that any precise thing aimed at would be destroyed. But the menace of the airship is strong in the minds of the people, especially in London. After one or two bomb-dropping experiments by the Germans from aeroplanes over Paris the Parisians discovered there was little danger from that sort of warfare, and watched the maneuvers of the German Tauben with interest but without much fear. However, the English have had no experiences as yet, and they are afraid of airships and of Zeppelins. The admiralty printed in all the London papers an intimation that an English airship, or several of them, might be flying over London after September first, and warning the people not to shoot at them if any came. If a German dirigible baloon should sail over the English metropolis some morning the

stampede to the cellars would be tre. mendous.

A man who was at Antwerp on the day the Zeppelin tried its second bombdropping experiment told me that the real danger was not from the bomb dropped, but from the attempts to bring down the baloon. Every Belgian soldier had been instructed to fire at any airship or dirigible that appeared, and so had the forts. The consequence was that, as soon as this dirigible did appear, every man who had a gun, or who controlled a cannon, began shooting straight up in the air; and the further consequence was that presently it began to rain bullets and shells in Antwerp.

The bullets did not hit the airship or anything else except the atmosphere; and after they had gone up as far as the force of the powder behind them would take them, they necessarily came back to earth. War writers have often spoken of a leaden hail. There was one in Antwerp that day. Many skylights in the place were broken, and the scramble to the cellars wounded more people than fifty dropped bombs would have.

An item of news that was not printed in the English papers, but that had wide circulation none the less, concerned an alleged statement by Count Zeppelin. He was asked when he intended to send some of his airships over to London. "That will come in due course," he is said to have replied. This, combined with statements that many new dirigibles and many more airships are being made. by Germany, caused considerable nervousness in London and made that warning by the Admiralty rather necessary; for all airships look alike to a scared community, and there is no doubt there would have been an attempt to destroy any that should appear.

Without gasoline, these huge armies would be practically helpless, for in a battle line as far flung as is the present one, and as will be the battle lines of the future if this battle is not decisive, the delay in communication would be fatal; in fact, such battles would be impossible, because of the lack of the mobility of the troops. It is true that the soldiers, after railroad trains have been used to their extreme advantage march many miles, just as did the troops of a hundred years ago, both in the

advance and in retreat; but the number of men engaged in any battle in the world's history was so much smaller than the number engaged in the battles of today that there can be no analogy drawn.

Gasoline is the most powerfully utilitarian of the nonhuman factories in this war. Without gasoline the present plan of war would be impossible. With gasoline, and the resultant uses of gasoline engines for every sort of propulsive demand, it is feasible for a general to attack with a million or two of men along a battle front of two or three hundred

miles, and for another general to defend with similar numbers.

With the aid of gasoline these vast armies can be fed and moved, kept in communication, and their numbers discovered and determined. A modern army travels on its gasoline. If you have watched the dispatches you will observe that the men in charge know this, for gasoline is the first on the list of stores to be commandeered, is first of the tributes demanded from the conquered people, and is more important than food. or ammunition, for without it food and ammunition would be tardy if not impossible.-Bessemer Monthly.

Progressive trials hitherto recorded have been confined almost exclusively to steampropelled craft, and very few of these have related to vessels under 50 feet in length, or of a total horsepower below 70 to 100. This is readily explained by the fact that in steam engines, the measurement of power by the use of the indicator becomes increasingly difficult, and the accuracy more doubtful, as the engine becomes smaller and the rotational speed higher. In addition to this, the staff of observers necessary for conducting a trail is virtually the same for a small as for a large vessel, if the operations are to be carried out, and the records made, simultaneously. For ordinary measured mile trials, each lasting from say four to seven minutes, according to the speed attained, the skill and accuracy required is of the highest order if the results are to be of any real scientific value. In many steam vessels of the size mentioned above, the space available for observers, and the conditions of working, are such as to make simultaneous records impossible, and when this is the case, estimated values have often to take the place of actual recorded figures.

The use of the internal-combustion engine of the small high-speed type, with from two to eight cylinders, puts the ordinary indicator out of the question for power measurement during trial runs; while to use other methods for measuring the power between engine and propeller is far from easy, and certainly cannot

be done without extensive preparations, while in most cases of small craft the passengers are limited to the helmsman and one observer.

Although at first sight the difficulties in the way of making progressive trials of motor boats may seem unusually serious, yet the importance of obtaining reliable data at the present time is so great that a reasonably accurate and, at the same time, simple method of carrying out such trials singlehanded is urgently needed. In the design of new boats, in the present struggle for greater speeds, and in the continually recurring problem of propeller efficiency, as well as the determination of the most economical speeds for various types of hulls, may be found the arguments for special exertions in this direction. In what follows the author proposes to describe a method of making speed and power tests of motor boats which has been in use for the past three years, and has proved uniformly successful, not the least of its good points being that all the work and observations can be done by one man. It cannot be used with single-cylinder engines, and its value is limited with two or three cylinders, but beyond this number excellent results can always be obtained.

The first stage commences at the test bench, on which the engine must be thoroughly "run in." A power curve is then obtained over the whole working range, from the lowest possible speed to something beyond that at which the en

gine will be run in the boat. When this has been done, similar curves are obtained, also over the whole range of revolutions, by cutting out cylinder by cylinder until only one is left. If all the cylinders are not of uniform power, the weaker ones must be "brought up" before carrying out these tests. If any doubt of their equality exists, careful note should be made of those cut out on each power curve, so that the same conditions may be subsequently reproduced in the boat. The method of The method of carrying out these tests on the bench presents many important and interesting features, and requires great care to execute if considerable accuracy is required. A series of curves from a four-cylinder engine are shown in Fig. 1.

When the engine is installed in the boat a reliable speed indicator is a necessary adjunct on the engine, and unless the friction clutch is combined with a positive drive, some means of counting the revolutions of the propeller-shaft also is absolutely essential. The author's experience of revolution-indicators has always been such as to make the use of the ordinary counter desirable as a check.

After the preliminary runs afloat have been made, and the highest speed of boat, engine and propeller ascertained, the next step is to cut out successively the cylinders corresponding with those cut out during the power measurements on the testbench. The cutting out must extend for a sufficiently long interval of time to ensure the boat settling down to its speed due to the power then being developed, the corresponding revolutions being carefully noted. It is essential that the adjustments of both throttle and ignition should be such as to obtain the highest revolutions the engine will give under these reduced powers, so that the testbench conditions may be carefully reproduced.

Having obtained the necessary data of the revolutions, the power co-ordinated can be picked off from the chart obtained on the test-bench, and the engine can then be run normally with all cylinders firing. It is unnecessary to carry out trials over the measured distance with any cylinders cut out. Further trials are next carried out at reduced. powers, the engine being run as nearly as possible at the revolution speeds obtained by cutting out the various cylinders. If intermediate speeds are required, the power developed may be es

timated as follows: On the base of revolutions per minute, horsepowers as obtained by cutting out the cylinders in the manner just described should be plotted. A fair curve drawn through these points will enable powers due to other propeller speeds to be closely estimated. This is shown in the curve A, B, C, D, Fig. 1.

By a combination of the data thus obtained a curve of horsepowers at various speeds of boat may be plotted. A curve of revolutions plotted on a base of speed in

knots supplies some of the necessary data for the analysis of the propeller. These curves are shown in Fig. 2. In boats having speeds of 20 knots and over, it is desirable, if possible, when running as low as 5 knots, to reduce proportionately the measured distance run. Thus, while a nautical mile is none too great for accurately timing at 20 knots, its length is liable to vitiate results at 5 knots unless the weather is absolutely calm and the currents uniform.

The errors which may occur by this method of estimating powers relative to

speeds are not of a nature to be a serious bar to future calculations or deductions for other boats. In the first place, the engine if well "run in" on the test-bench, is not likely to develop more brake power when in the boat than while on the bench, while actually the power delivered to the screw will be less by reason of losses in the reverse gear, tail-shaft bearings, and stuffing boxes. These however, will naturally be greater when the boat is first launched than when, after a few hours' running, all these parts have become "worked in." In the next place, such losses will occur in all installations, so that the question of total brake horsepower of the engine is, for future calculation, more important than net power to the screw. Errors due to a slipping clutch are more serious, but the provision of a counter on the propeller shaft, as well as on the engine, is a check to this.

The author, while quite aware that the method just described cannot be consid

AMERICAN TRACTORS

Think of an American gasoline caterpillar tractor hauling a German siege gun. These powerful guns were the surprise of the European war. The secret of their existence was closely guarded by Germany and this photograph was secured at the risk of being shot as a spy. The gun weighs over 30 tons and it is stated that practically ever caterpillar tractor and all other gasoline tractors and motor trucks in Europe have been confiscated for war use.

ered as one of absolute scientific accuracy, has thoroughly satisfied himself of the utility of the method and its value in designing new boats and installations.

The curves in Figs. 1 and 2 relate to an early type of speed boat of 26 feet in length, with a set of four-cylinder engines installed, but they are given to show the process rather than for any special information which they contain. The author has made a series of trials of boats, which he hopes shortly to publish, with some deductions therefrom as to the relationship of speed and power. One thing may be added to the above. The most valuable information which can possibly be obtained in progressive trials is what is, fortunately, the most easy to observe-namely, the relationship between revolutions per minute of the screw and speed of the vessel. Many years of study of the screw-propellor have shown the author that very definite laws are associated with this relationship. -Engineering (London).