Rival Motive Powers.
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One frequently hears the opinion given, and more often than not by persons innocent of motor experience, that the internal combustion engine has already relegated the steam engine to second place in commercial motoring. The fact that the petroleum spirit engine is first, and the rest nowhere, in the field of pleasure or touring cars, is largely accountable. for this prevalent view. A genuine conviction on this subject is engendered, too, as regards even the most superficial observer of events, by the great preponderance of the newer method of deriving power which is found in the prime movers upon the popular motor omnibuses of to-day ; and this last fact, more than all the rest put together, is calculated to boom the explosion motor at the expense of the steam engine. But it is early in the contest to accept present experience as indicating any finality in respect of the ultimate ratios between steam-propelled and petrol-engined vehicles. Further, some account will have to be taken of accumulator propulsion ; for example, the wide employment of secondary batteries in New York City, as the portative source of motive power for large observation cars, has already led to valuable improvements. We find that systematised methods of re-charging and suspending the boxes, coupled with more careful supervision and examination, have resulted in a greatly increased life for the cells which, under such favourable treatment, retain eighty per cent. of their original capacity after twelve months' use. But the best results obtained to date in this direction exhibit costs for power which are much above those for either steam or internal combustion engines. The one other system which falls within the range of practical politics is that colloquially termed the "
petrol. electric," in which an internal combustion engine is employed in conjunction with a dynamo and one or more electric motors. The huge and unwieldly proportions of the earlier petrol-electric chassis have gradually been replaced by more graceful and compact combinations, until we find a great city like Vienna on the point of condemning practically
the whole of its municipal fire brigade horsed vehicles and arranging for the immediate adoption of petrol-electric vehicles. Given the absence of necessity for cells, which are now almost universally supplied as an essential part of any such system, we look upon the prospects of these vehicles as being exceptionally bright. We have before us the confidential details of a petrol-electric system from which all cells are eliminated, suitable and effective provision for starting being made without necessity for recourse to their aid. In this arrangement, one sees that the internal combustion engine is, indeed, supreme, and that the electric elements are made dependent upon and subsidiary to it. Any examination into the relative merits of steam, petrol, accumulator or petrol-electric propulsion reveals the fact that each has its spheres of application. Where the guiding consideration is commercial efficiency, it is imperative that users should be ever on the alert to apply the system or systems best adapted to the demands of their customers and the circumstances of the particular routes to be covered. Accepting these conditions as sound, we can discover no evidence to support the somewhat wild claims that the petrol engine per se will become universal. Manufacturers themselves, better than any, know the difficulties which arise when petrol engines are mounted in frames carried on non-resilient tyres, and how the advantages of regular service and economy in tare weight are jeopardised by such ambition. It so happens that the specification for a double-deck omnibus approaches the limits which govern the successful use of the petrol engine, for when rubber tyres have to be discarded, and when a 40 or 5oh.p. engine has to be fitted in order to cope with the increased demands which are consequent upon steel tyres, greater tare, and heavier loads, it is better to rely upon steam power as a rule. The exceptions are where difficulties over water and fuel supply outweigh the advantage of a more flexible engine and transmission. On the other hand, to quote one instance of many, steam may be preferable in certain parts of the world, how
ever difficult it may be to obtain water, if a sand-laden atmosphere renders the essential draughts of air a source of scored cylinders. The fact that water provides a pure medium to work inside the engine must often cause a preference to be accorded it over the internal combustion engine which is dependent for its working upon an external medium as well as the fuel proper The petrol engine will prove best for loads below 34 tons, but steam will have a material share within that range. For heavier loads, steam is superior. Accumulator propulsion will always be limited to charging centres, but in the petrolelectric system the greatest possibilities of development lie.