We will suppose that the engine is just starting. The pistons are in a position nearest to the crank-case. As they separate they draw a charge—equal in volume to double the cubical contents of one cylinder—into the crank-case through its inlet valve. During the return stroke the charge is squeezed, and passes through a valve into a chamber which forms, as it were, the fourth spoke of a four-spoked wheel, of which the other three spokes are the cylinders and the "silencer." This chamber is connected by pipes to the inlet valves of the cylinders, which are mechanically opened alternately by the action of special cams on the crank-shaft. The cylinder which gets the contents of the compression chamber receives considerably more "mixture" than would flow in under natural suction, and the compression is therefore greater than in the ordinary type of cycle motor, and the explosion more violent. Hence it comes about that the cylinders, which have a bore of only 2 in. and a 2-in. stroke for the piston, develop nearly 2 h.p. each.
It may at first appear rather mysterious how, if the cranks are rigidly attached to the cycle frame, any motion can be imparted to the driving-wheel. The explanation is simple enough: a belt pulley is affixed to one side of the crank-case, and revolves with the cylinders, the silencer, and compression chamber. The rotation is caused by the effort of the piston to get as far as possible away from the closed end of the cylinder after an explosion. Where a crank is movable but the cylinder fixed, the former would be turned round; where the crank is immovable but the cylinder movable, the travel of the piston is possible only if the cylinder moves round the crank. A series of explosions following one another in rapid succession gives the moving parts of the Barry engine sufficient momentum to suck in charges, compress them, and eject the burnt gases. The plan is ingenious, and as the machine into which this type of engine is built weighs altogether only about 70 lbs., the "sport" of motor cycling is open to those people whose age or want of strength would preclude them from the use of the heavy mounts which are still to be seen about the roads. In the future we may expect to find motor cycles approach very closely to a half-hundredweight standard without sacrificing the rigidity needful for fast locomotion over second-class roads.
For "pace-making" on racing tracks, motor cycles ranging up to 24 h.p. have been used; but these are essentially "freak" machines of no practical value for ordinary purposes. Even 3-4 h.p. cycles have set up wonderful records, exceeding fifty miles in the hour, a speed equal to that of a good express train. In comparison with the feats of motor-cars, their achievements may not appear very startling; but when we consider the small size and weight, and the simplicity of the mechanisms which propel cycle and rider at nearly a mile a minute, the result seems marvellous enough.
During the last few years the tricycle has again come into favour, but with the arrangement of its wheels altered; two steering-wheels being placed in front, and a single driving-wheel behind. The main advantage of this inversion is that it permits the fixing of a seat in front of the driver, in which a passenger can be comfortably accommodated. The modern "tricar," with its high-powered, doubled-cylindered engines, its change-speed gears, its friction clutch for bringing the engines gradually into action, its forced water circulation for cooling the cylinders, and its spring-hung frame, is in reality more a car than a cycle, and escapes from the former category only on account of the number of its wheels. To the tourist, or to the person who does not find pleasure in solitary riding, the tricar offers many advantages, and, though decidedly more expensive to keep up than a motor bicycle, entails only very modest bills in comparison with those which affect many owners of cars.
The development of the motor cycle has been hastened and fostered by frequent speed and reliability contests, in which the nimble little motor has acquitted itself wonderfully. A hill a mile long, with very steep gradients, has been ascended in considerably less than two minutes by a 3 1 / 4 h.p. motor. We read of motor cycles travelling from Land's End to John-o'-Groats; from Calcutta to Bombay; from Sydney to Melbourne; from Paris to Rome—all in phenomenal times considering the physical difficulties of the various routes. Such tests prove the endurance of the motor cycle, and pave the way to its use in more profitable employments. Volunteer cycling corps often include a motor or two, which in active service would be most valuable for scouting purposes, especially if powerful enough to tow a light machine-gun. Commercial travellers, fitting a box to the front of a tricar, are able to scour the country quickly and inexpensively in quest of orders for the firms they represent. The police find the motor helpful for patrolling the roads. On the Continent, and especially in Germany, town and country postmen collect and deliver parcels and letters with the aid of the petrol-driven tricycle, and thereby save much time, while improving the service. Before long, "Hark 'tis the twanging horn" will once again herald the postman's approach in a thousand rural districts, but the horn will not hang from the belt of a horseman, such as the poet Cowper describes, but will be secured to the handle-bars of a neat tricar. Thus history repeats itself.
Photo] [Cribb, Southsea.
A MOTOR LAWN-MOWER
A machine of this kind will cut several acres a day, and also acts as an efficient roller. The operator is able to empty the contents of the catch-box without leaving his seat.
That the motor cycle is still far from perfect almost goes without saying; but every year sees a decided advance in its design and efficiency. The messy, troublesome accumulator will eventually give way to a neat little dynamo, which is driven by the engine and creates current for exploding the cylinder charges as the machine travels. When the cycle is at rest there would then be no fear of electricity leaking away through some secret "short circuit," since the current ceases with the need for it, but starts again when its presence is required. The proper cooling of the cylinders has been made an easier matter than formerly by the introduction of fans which direct a stream of cold air on to the cylinder head. Professor H. L. Callendar has shown in a series of experiments that a fan, which absorbs only 2 to 3 per cent. of an engine's power, will increase the engine's efficiency immensely when a low gear is being used for hill climbing, and the rate of motion through the air has fallen below that requisite to carry off the surplus heat of the motor. If an engine maintains a good working temperature when it progresses through space two feet for every explosion, it would overheat if the amount of progression were, through the medium of a change-gear attachment, reduced to one foot, a change which would be advisable on a steep hill. The fan then supplies the deficiency by imitating the natural rush of air. As Professor Callendar says: "The most important point for the motor cyclist is to secure the maximum of power with the minimum of weight. With this object, the first essentials are a variable speed gear of wide range, and some efficient method of cooling to prevent overheating at low gears.... It is unscientific to double the weight and power of the machine in order to climb a few hills, when the same result can be secured with a variable gear. It is unnecessary to resort to the weight and complication of water cooling when a light fan will do all that is required."