The existing keen motor-car rivalry presents one of the most interesting and instructive mechanical problems which are left still unsolved by the close of the nineteenth century. The question to be determined is not so much whether road locomotion by means of mechanical power is practicable and useful, for, of course, that point has been settled long ago; indeed it would have been recognised as settled years before had it not been for the cra.s.s legislation of a quarter of a century since which deliberately drove the first steam-motors off the road in order to ensure the undisturbed supremacy of horse traffic. The real point at issue is whether a motor can be made which shall furnish power for purposes of road locomotion as cheaply and conveniently as is already done for stationary purposes.
Horse traction, although extremely dear, possesses one qualification which until the present day has enabled it to outdistance its mechanical compet.i.tors upon ordinary roads. This is its power of adapting itself, by special effort, to the exigencies caused by the varying nature of the road. Watch a team of horses pulling a waggon along an undulating highway, with level stretches of easy going and here and there a decline or a steep hill. There is a continual adjustment of the strain which each animal puts upon itself according to the character of the difficulties which must be surmounted, the effort varying from nothing at all--when going down a gentle decline--up to the almost desperate jerk with which the vehicle is taken over some stony part right on the brow of an eminence. The whip cracks and by threats and encouragements the driver induces each horse to put forth, for one brief moment, an effort which could not be sustained for many minutes save at the peril of utter exhaustion.
When the unit of nominal horse-power was fixed at 33,000 foot-pounds per minute the work contemplated in the arbitrary standard was supposed to be such as a horse could go on performing for several hours. It was, of course, well recognised that any good, upstanding horse, if urged to a special effort, could perform several times the indicated amount of work in a minute.
Nevertheless the habit of reckoning steam-power in terms of a unit drawn from the a.n.a.logy of the horse undoubtedly tended for many years to obscure the essential difference between the natures of the two sources of power. Railroads were built with the object of rendering as uniform as possible the amount of power required to transport a given weight of goods or pa.s.sengers over a specified distance; and consequently the application of the steam-engine to traffic conducted on the railway line was a success. Many inventors at once jumped to the conclusion that, by making some fixed allowance for the greater roughness of an ordinary road, they would be able to construct a steam-traction engine that would suit exactly for road traffic. In a rough and rudimentary way an attempt to provide for the special effort required at steep or stony places was made by the introduction of a kind of fly-wheel of extraordinary weight proportionate to the size of the engine; and the same object was aimed at by increasing the power of the engine to somewhere near the limit of the possible special requirements. The consequence was the evolution of an immensely ponderous and wasteful machine, which for some years only held its ground within the domain of the heavy work of roadmaking. As a means of road traction the steam-engine was for half a century almost entirely discomfited and routed by horse-power, partly owing to this mechanical defect and partly, as we have seen, through legislative partisanship.
The explosive type of engine was next called into requisition to do battle against the living compet.i.tor of the engineer"s handiwork.
Petroleum and alcohol, when volatilised and mixed with air in due proportion, form explosive mixtures which are much more nearly instantaneous in their action than an elastic vapour like steam held under pressure in a boiler, and liberated to perform its work by comparatively slow expansion. The petroleum engine, as applied to the automobile, does its work in a series of jerks which provide for the unequal degrees of power required to cope with the unevenness of a road.
As against this, however, there are certain grave defects, due mainly to the use of highly inflammable oils vapourised at high temperatures; and these have impressed a large proportion of engineers with a belief that, in the long run, either electricity or steam will win the day.
Storage batteries are well adapted for meeting the exigencies of the road, just as they are for those of tramway traffic, because, as soon as an extra strain is to be met, there is always the resource of coupling up fresh batteries held in reserve--a process which amounts to the same as yoking new horses to the vehicle in order to take it up a hill. In practice, however, it is found that the jerky vibratory motion of the gasoline automobile provides for this in a way almost as convenient, although not so pleasant.
The chance of the steam-engine being largely adopted for automobile work and for road traffic generally depends princ.i.p.ally on the prospects of inventing a form of cylinder--or its equivalent--which will enable the driver to couple up fresh effective working parts of his machinery at will, just as may be done with storage batteries. A new form of steam cylinder designed to provide for this need will outwardly resemble a long pipe--one being fixed on each lower side of the vehicle--but inwardly it will be divided into compartments each of which will have its own separate piston. Practically there will thus be a series of cylinders having one piston-rod running through them all, but each having its own piston.
Normally, this machine will run with an admission of steam to only one or two of the cylinders; but when extra work has to be done the other cylinders will be called into requisition by the opening of the steam valves leading to them. Provision can be made for the automatic working of this adjustment by the introduction of a spring upon the piston-rod, so arranged that, as soon as the resistance reaches a certain point, a lever is actuated which opens the valves to admit steam to the reserve cylinders of the engine. On such occasions, of course, the consumption of steam must necessarily be greatly increased; but on the other hand the automatic system of the admission to each cylinder also results in a shutting off of the steam when little or no work is required. In fact, with a fully automatic action, regulating the consumption of steam exactly according to the amount of force necessary to drive the automobile, it would be possible to work even a single cylinder to much greater advantage than is done by the machines generally in use.
So heavy are the storage batteries needed for electric traction of the road motor-car that practically it is not found convenient to carry enough of cells to last for more than a twenty-mile run. The batteries must then either be replaced, or a delay of some three hours must occur while they are being recharged. The idea of establishing charging stations at almost every conceivable terminus of a run is quite chimerical; and, even if hundreds of such stations were provided for the convenience of the users of electric traction, the limitation imposed by being forced to follow the established routes would always give to the non-electric motor an advantage over its compet.i.tor.
The best hope for the storage battery on the automobile rests upon its convenience as a repository of reserve power in conjunction with such a prime motor as the steam-engine. A turbine worked by a jet of steam, as already described, and moving in a magnetic field to generate electricity for storage in a few cells, is a convenient form in which steam and electricity can be yoked together in order to secure a power of just the type suitable for driving an automobile. In the machine indicated the supply of the motive power is direct from the storage batteries, which can be coupled up in any required number according to the exigencies of the road. Automatic gear may be introduced by an adaptation of the principle already referred to.
In a light road-motor for carrying one or two persons on holiday trips or business rounds, the quality of adaptability of the source of power to the sudden demands due to differences of level in the road is not so absolutely essential as it is in traction engines designed for the transport of goods over ordinary roads. In the former cla.s.s of work the waste of power involved in employing a motor of strength sufficient to climb hills--although the bulk of the distance to be travelled is along level roads--may not be at all so serious as to overbalance the many and manifest advantages of the automobile principle. At the same time, as has already been indicated, there is no doubt whatever that when proper automatic shut-off contrivances have been applied for economising mechanical energy in the pa.s.senger road-motor, an immense impetus will be given to its advancement.
In the road traction-engine the need for what may be termed _effort_ on the part of the mechanism is much greater, more especially as the compet.i.tion against horse-traction is conducted on terms so much more nearly level. A team of strong draught-horses driven by one man on a well-loaded waggon is a far more economical installation of power than a two-horse buggy carrying one or two pa.s.sengers.
The asphalt and macadamised tracks which are now being laid down along the sides of roads for the convenience of cyclists, are the significant forerunners of an improvement destined to produce a revolution in road traffic during the twentieth century. When automobiles have become very much more numerous, and local authorities find that the settlement of wealthy or comparatively well-to-do families in their neighbourhoods may depend very largely upon the question whether light road-motor traffic may be conveniently conducted to and from the nearest city, an immense impetus will be administered to the reasonable efforts made for catering for the demand for tracks for the accommodation of automobiles, both private and public.
The tyranny of the railway station will then be to a large extent mitigated, and suburban or country residents will no longer be practically compelled to crowd up close to each station on their lines of railroad. Under existing conditions many of those who travel fifteen or twenty miles to business every day live just as close to one another, and with nearly as marked a lack of s.p.a.ce for lawn and garden, as if they lived within the city. The bunchy nature of settlement promoted by railways must have excited the notice of any intelligent observer during the past twenty or thirty years--that is to say since the suburban railroad began to take its place as an important factor in determining the locating of population.
To a very large extent the automobile will be rather a feeder to the railway than a rival to it; and all sorts of by-roads and country lanes will be improved and adapted so as to admit of residents running into their stations by their own motor-cars and then completing their journeys by rail. But when this point has been reached, and when fairly smooth tracks adapted for automobile and cycling traffic have been laid down all over the country, a very interesting question will crop up having reference to the practicability of converting these tracks into highways combining the capabilities both of roads and of railways.
In an ordinary railroad the functions of the iron or steel rails are twofold, first to carry the weight of the load, and second to guide the engine, carriage or truck in the right direction. Now the latter purpose--in the case of a rail-track never used for high speeds, especially in going round curves--might be served by the adoption of a very much lighter weight of rail, if only the carrying of the load could be otherwise provided for. In fact, if pneumatic-tyre wheels, running on a fairly smooth asphalt track, were employed to bear the weight of a vehicle, there would then be no need for more than one guide-rail, which might readily be fixed in the middle of the track; but this should preferably be made to resemble the rail of a tram rather than that of a railroad.
"Every man his own engine-driver" will be a rule which will undoubtedly require some little social and mechanical adjustment to carry out within the limits of the public safety. But the automobile, even in its existing form, makes the task of completing this adjustment practically a certainty of the near future; and as soon as it is seen that motor tracks with guide lines render traffic safer than it is on ordinary roads, the main objections to the innovation will be rapidly overcome. The rule of the road for such guide-line tracks will probably be based very closely on that which at present exists for ordinary thoroughfares. On those roads where two tracks have been laid down each motor will be required to keep to the left, and when a traveller coming up behind is impatient at the slow rate of speed adopted by his precursor he will be compelled to make the necessary detour himself, pa.s.sing into the middle of the thoroughfare and there outstripping the party in front, without the a.s.sistance of the guide-rail, and rejoining the track.
To execute this movement, of course, the motor wheels for the guide-tracks must be mounted on entirely different principles from those adapted for railroad traffic. The broad and soft tyred wheels which bear upon the asphalt track will be entrusted with the duty of carrying the machine without extraneous aid; but there will be two extra wheels, one in front and one at the rear, capable of being lifted at any time by means of a lever controlled by the driver. These guiding wheels will fit into the groove of the tram line in the centre, being made of a shape suitable for enabling the driver to pick up the groove quickly whenever he pleases. The carrying wheels of the vehicle in this system are enabled to pa.s.s over the guide-rail readily, because the latter does not stand up from the track like the line in a railroad.
A simpler plan, particularly adapted for roads which are to have only a single guide-rail, is to place the rail at the off-side of the track, and to raise it a few inches from the ground. The wheels for the rail are attached to arms which can be raised and lifted off the rail by the driver operating a lever. Guiding irons, forming an inverted Y, are placed below the bearings of the wheels to facilitate the picking up of the rail, their effect being that, if the driver places his vehicle in approximately the position for engaging the side wheels with the rail and then goes slowly ahead, he will very quickly be drawn into the correct alignment. Of course the rails for this kind of track can be very light and inexpensive in comparison with those required for railroads on which the whole weight of each vehicle, as well as the lateral strain caused by its guidance, must fall upon the rail itself.
The asphalt track and its equivalent will be the means of bringing much nearer to fulfilment the dream of having "a railway to every man"s door". Many such tracks will be equipped with electric cables as well as guiding-rails, so that cars with electric motors will be available for running on them, and the power will be supplied from a publicly-maintained station. Some difficulty may at first be experienced in adjusting the rates and modes of payment for the facilities thus offered; but a convenient precedent is present to hand in the cla.s.s of enactment under which tramway companies are at present protected from having their permanent ways used by vehicles owned by other persons. Practically the possession of a vehicle having a f.l.a.n.g.ed wheel and a gauge exactly the same as that of the tram lines in the vicinity may be taken to indicate an intention to use the lines. Similarly a certain relation between the positions of guiding wheels and those of the connections with cables may be held to furnish evidence of liability to contribute towards the maintenance of motor-tracks.
Roads and railways will be much more closely inter-related in the future than they have been in the past. The compet.i.tion of the automobile would in itself be practically sufficient to force the owners of railways into a more adaptive mood in regard to the true relations between the world"s great highways. The way in which the course of evolution will work the problem out may be indicated thus:--First, the owners of automobiles will find it convenient in many instances to run by road to the nearest railway station which suits their purposes, leaving their machines in charge of the stationmaster and going on by train. In course of time the owners of "omnibus automobiles" will desire to secure the same advantage for their customers, and on this account the road cars will await the arrival and departure of every train just as horse vehicles do at present. The next step will be taken by the railway companies, or by the local authorities, when it becomes obvious that there is much more profit in motor traffic than there ever was in catering for the public by means of vehicles drawn by horses. Each important railway station will have its diverging lines of motor-traffic for the convenience of pa.s.sengers, some of them owned and managed by the same authority as the railway line itself.
Rivalry will shortly enforce an improvement upon this system, because in the keen compet.i.tion between railway lines those stations will attract the best parts of the trade at which the pa.s.sengers are put to the smallest amount of inconvenience. The necessity for changing trains, with its attendant bustle of looking after luggage, perhaps during very inclement weather, always acts as a hindrance to the popularity of a line. When "motor-omnibuses" are running by road all the way into the city, setting people down almost at their doors and making wide circuits by road, the proprietors of these vehicles will make the most of their advantages in offering to travellers a cosy and comfortable retreat during the whole of their journey.
Road-motors, comfortably furnished, will therefore be mounted upon low railway trucks of special construction, designed to permit of their being run on and off the trucks from the level of the ground. The plan of mounting a road vehicle upon a truck suited to receive it has already been adopted for some purposes, notably for the removal of furniture and similar goods; and it is capable of immense extension.
An express train will run through on the leading routes from which roads branch out in all directions, and as it approaches each station it will uncouple the truck and "motor-omnibus" intended for that destination. The latter will be shunted on to a loopline. The road-motor will be set free from its truck and will then proceed on its journey by road.
When a similar system has been fully adapted for the conveyance of goods by rail and road experiments will then be commenced, on a systematic basis, with the object of rendering possible the picking up of packages, and even of vehicles, without stopping the train. The most pressing problem which now awaits solution in the railway world is how to serve roadside stations by express trains. "Through"
pa.s.sengers demand a rapid service; while the roadside traffic goes largely to the line that offers the most frequent trains. In the violent strain and effort to combine these two desiderata the most successful means yet adopted have been those which rely upon the destruction of enormous quant.i.ties of costly engine-power by means of quick-acting brakes. The amount of power daily converted into the mischievous heat of friction by the brakes on some lines of railway would suffice to work the whole of the traffic several times over; but the sacrifice has been enforced by the public demand for a train that shall run fast and shall yet stop as frequently as possible.
Progress in this direction has reached its limit. A brake that shall conserve, instead of destroying, the power of the train"s inertia on pulling up at a station is urgently required; but the efforts towards supplying the want have not, so far, proved very successful. Each carriage or truck must be fitted with an air-pump so arranged that, on the application of the brake by the engine-driver, it shall drive back a corresponding amount of air to that which has been liberated from the reservoir, and the energy thus stored must be rendered available for re-starting the train. Trials in this direction have been made through the application of strong springs which are caused to engage upon the wheels when the brake is applied, and thus are wound up, but which may then be reversed in position, so that for the starting of the vehicle the rebound of the spring offers material a.s.sistance. It is obvious, however, that the use of compressed air harmonises better with the railway system than any plan depending upon springs. The potential elasticity in an air-reservoir of portable dimensions is enormously greater than that of any metallic spring which could conveniently be carried.
In picking up and setting down mail-bags a system has been for some years in operation on certain railway lines indicating in a small way the possibilities of the future in the direction of obviating the need for stopping trains at stations. The bag is hung on a sliding rod outside of the platform, and on a corresponding part of the van is affixed a strong net, which comes in contact with the bag and catches it while the train goes past at full speed. Dropping a bag is, of course, a simpler matter.
The occasionally urgent demand for the sending of parcels in a similar manner has set many inventive brains to work on the problem of extending the possibilities of this system, and there seems no reason to doubt that before long it will be practicable to load some cla.s.ses of small, and not readily broken, articles into trucks or vans while trains are in motion.
The root idea from which such an invention will spring may be borrowed from the sliding rail and tobogganing devices already introduced in pleasure grounds for the amus.e.m.e.nt of those who enjoy trying every novel excitement. A light and very small truck may be caused to run down an incline and to throw itself into one of the trucks comprising a goods train. The method of timing the descent, of course, will only be definitely ascertained after careful calculation and experiments designed to determine what length of time must elapse between the liberation of the small descending truck and the pa.s.sing of the vehicle into which its contents are to be projected.
Foot-bridges over railway lines at wayside stations will afford the first conveniences to serve as tentative appliances for the purpose indicated. From the overway of the bridge are built out two light frameworks carrying small tram-lines which are set at sharp declivities in the directions of the up and the down trains respectively, and which terminate at a point just high enough to clear the smoke-stack of the engine.
The small truck, into which the goods to be loaded are stowed with suitable packings to prevent undue concussion, is held at the top of its course by a catch, readily released by pressure on a lever from below. The guard"s van is provided at its front end with a steel, upright rod carrying a cross-piece, which is easily elevated by the guard or his a.s.sistant in antic.i.p.ation of pa.s.sing any station where parcels are to be received by projection. At the rear of the van is an open receptacle communicating by a door or window with the van itself.
At the instant when the steel cross-piece comes in contact with the lever of the catch, which holds the little truck in position on the elevated footbridge, the descent begins, and by the time that the receptacle behind the van has come directly under the end of the sloping track the truck has reached the latter point and is brought to a sudden standstill by buffers at the termination of the miniature "toboggan". The ends of the little truck being left open, its contents are discharged into the receptacle behind the van, from which the guard or a.s.sistant in charge removes them into the vehicle itself. For catching the parcels thrown out from the van a much simpler set of apparatus is sufficient.
On a larger scale, no doubt in course of time, a somewhat similar plan will be brought into operation for causing loaded trucks to run from elevated sidings and to join themselves on to trains in motion. One essential condition for the attainment of this object is that the rails of the siding should be set at such a steep declivity that, when the last van of the pa.s.sing train has cleared the points and set the waiting truck in motion by liberating its catch, the rate of speed attained by the pursuing vehicle should be sufficiently high to enable it to catch the train by its own impetus.
It may be found more convenient on some lines to provide nearly level sidings and to impart the necessary momentum to the waiting truck, partly through the propelling agency of compressed air. Any project for what will be described as "shooting a truck loaded with valuable goods after the retreating end of a train," in order to cause it to catch up with the moving vehicles, will no doubt give rise to alarm; and this feeling will be intensified when further proposals for projecting carriages full of pa.s.sengers in a similar method come up for discussion. But these apprehensions will be met and answered in the light of the fact that in the earlier part of the nineteenth century critics of what was called "Stephenson"s mad scheme" of making trains run twenty or even thirty miles an hour were gradually induced to calm their nerves sufficiently to try the new experience of a train journey!
The wire-rope tramway has. .h.i.therto been used princ.i.p.ally in connection with mines situated in very hilly localities. Trestles are erected at intervals upon which a strong steel rope is stretched and this carries the buckets or trucks slung on pulley-blocks, contrived so as to pa.s.s the supports without interference. A system of this kind can be worked electrically, the wire-rope being employed also for the conveyance of the current. But an inherent defect in the principle lies in the fact that the wire-rope dips deeply when the weight pa.s.ses over it, and thus the progress from one support to another resolves itself into a series of sharp descents, followed by equally sharp ascents up a corresponding incline. The usual way of working the traffic is to haul the freight by means of a rope wound round a windla.s.s driven by a stationary engine at the end. The constantly varying strain on the cable proves how large is the amount of power that must be wasted in jerking the buckets up one incline to let them jolt down another when the point of support has been pa.s.sed.
Hitherto the wire-rope tramway has been usually adopted merely as presenting the lesser of two evils. If the nature of the hills to be traversed be so precipitous that ruinous cuttings and bridges would be needed for the construction of an ordinary railway or tramway line, the idea of conveyance by wire suggests itself as being, at least, a temporary mode of getting over the difficulty. But a great extension of the principle of overhead haulage may be expected as soon as the dipping of the load has been obviated, and the portion of the moving line upon which it is situated has been made rigid. A strong but light steel framework, placed in the line of the drawing-cable, and of sufficient length to reach across two of the intervals between the supports, may be drawn over enlarged pulleys and remain quite rigid all the time.
The weight-carrying wire-rope is thus dispensed with, and the installation acquires a new character, becoming, in point of fact, a moving bridge which is drawn across its supports and fits into the grooves in the wheels surmounting the latter. The carriage or truck may be constructed on the plan adopted for the building of the longest type of modern bogie carriages for ordinary railways, the tensile strength of steel rods being largely utilised for imparting rigidity.
We now find that instead of a railway we have the idea of what may be more appropriately called a "wheelway". The primitive application of the same principle is to be seen in the devices used in dockyards and workshops for moving heavy weights along the ground by skidding them on rollers. Practically the main precaution observed in carrying out this operation is the taking care that no two rollers are put so far apart that the centre of gravity of the object to be conveyed shall have pa.s.sed over one before the end has come in contact with the next just ahead of it.
The "wheelway" itself will be economical in proportion as the length of the rigid carriage or truck which runs upon it is increased. The carrying of cheap freight will be the special province of the apparatus, and it will therefore be an object to secure the form of truck which will give, with the least expense, the greatest degree of rigidity over the longest stretch of span from one support to another.
Some modification of the tubular principle will probably supply the most promising form for the purpose. The hope of this will be greatly enhanced through the recent advances in the art of tube-constructing by which wrought-iron and tough steel tubes can be made quite seamless and jointless, being practically forged at one operation in the required tubular shape.
For mining and other similar purposes, the long tubal "wheelway"
trucks of this description can be drawn up an incline at the loading station so as to be partially "up-ended" in position for receiving the charges or loads of mineral or other freight. After this they can be despatched along the "wheelway" on the closing of the door at the loading end. In regard to the mode of application of the power in traction, the shorter-distance lines may serve their objects well enough by adopting the endless wire-rope system at present used on many mining properties.
But it is found in practice that for heavy freight this endless cable traction does not suit over distances of more than about two miles.
Mining men insist upon the caution that where this length of distance has to be exceeded in the haulage of ore from the mine over wire-rope tramways, there is need for two installations, the loaded trucks being pa.s.sed along from one to the other by means of suitable appliances at the termini.
Electric traction must, in the near future, displace such a c.u.mbrous system, and the plan upon which it will be applied will probably depend upon the use of a steel cable along which the motor-truck must haul itself in its progress. This cable will be kept stationary, but gripped by the wheels and other appliances of the electric motors with which the long trucks are provided. Besides this there must also be the conducting cables for the conveyance of the electric current.
For cheap means of transport in spa.r.s.ely-developed country, as well as in regions of an exceptionally hilly contour, the "wheelway" has a great future before it. Ultimately the system can be worked out so as to present an almost exact converse of the railway. The rails are fixed on the lower part of the elongated truck, one on each side; while the wheels, placed at intervals upon suitable supports, const.i.tute the permanent way. The amount of constructional work required for each mile of track under this plan is a mere fraction of that which is needed for the permanent way and rolling stock of a railway, the almost entire absence of earth-works being, of course, a most important source of economy.
Probably the development of transport on the principles indicated by the evolution of the ropeway or wire-rope tramway will take place primarily in connection with mining properties, and for general transport purposes in country of a nature which renders it unsuitable for railway construction. This applies not merely to hilly regions, but particularly to those long stretches of sandy country which impede the transport of traffic in many rich mining regions, and in patches separating good country from the seaboard. In the "wheelway" for land of this character the wheels need not be elevated more than a very few feet above the ground, just enough to keep them clear of the drift sand which in some places is fatal to the carrying out of any ordinary railway project.
The conception of a truck or other vehicle that shall practically carry its own rail-road has been an attractive one to some inventive minds. In sandy regions, and in other places where a railway track is difficult to maintain, and where, at any rate, there would hardly be sufficient traffic to encourage expenditure in laying an iron road, a very great boon would be a kind of motor which would lay its own rails in front of its wheels and pick them up again as soon as they had pa.s.sed.
A carriage of this kind was worked for some time on the Landes in France. The track was virtually a kind of endless band which ran round the four wheels, bearing a close resemblance to the ramp upon which the horse is made to tread in the "box" type of horse-gear. Several somewhat similar devices have been brought out, and a gradual approach seems to have been made towards a serviceable vehicle.
A large wheel offers less resistance to the traction of the weight upon it than a small one. The princ.i.p.al reason for this is that its outer periphery, being at any particular point comparatively straight, does not dip down into every hollow of the road, but strikes an average of the depressions and prominences which it meets. The pneumatic tyre accomplishes the same object, although in a different way, the weight being supported by an elastic surface which fits into the contour of the ground beneath it; and the downward pressure being balanced by the sum total of all the resistant forces offered by every part of the tyre which touches the ground, whether resting on hollows or on prominences.
Careful tests which have been made with pneumatic-tyred vehicles by means of various types of dynamometer have proved that, altogether apart from the question of comfort arising from absence of vibration, there is a very true and real saving of actual power in the driving of a vehicle on wheels fitted with inflated tubes, as compared with the quant.i.ty that is required to propel the same vehicle when resting on wheels having hard unyielding rims. So far as cycles and motor-cars are concerned, this is the best solution of the problem of averaging the inequalities of a road that has yet been presented; but when we come to consider the making of provision for goods traffic carried by traction engines along ordinary roadways, the difficulties which present themselves militating against the adoption of the pneumatic principle--at any rate so long as a cheap subst.i.tute for india-rubber is undiscovered--are practically insurmountable.