The propulsion of tram-cars by some motive power other than that supplied by horses has long constituted a tempting subject for inventors. Many attempts have been made to get rid of horses, and it must be confessed, with very limited success. To the amateur it appears to be absurd to employ horses when a little engine not much bigger than a coffee pot ought to be able to do the required work; and, besides, it would be so much nicer to propel a car by steam or compressed air than by horses, who suffer much in very hot and very cold weather — things of which an engine would take no cognisance. Engineers see nothing particularly tempting in the propulsion of tram-cars by machinery. The question presents itself solely in the light of a speculation to them, and the very first point which demands their consideration is one which the amateur ignores altogether. Will it pay to use steam, or ammonia, or compressed air ? On this point there happens to be no small diversity of opinion, and it must be admitted that the available stock of experience as to the working of tram-cars by steam is so small that it is difficult to say whether a saving may or not be reasonably expected. A line of tramway worked with cars, each drawn by one horse, requires a stud of about five horses per car to work, say, 13 hours a day. Each two-horse tram-car requires about nine and a half horses, experience going to show that the proportion of horse-power per car is rather less than doubled by using two horses instead of one. Assuming that the horses cost on an average £40 each, it follows that a double tram-car can be horsed for, say, £380. Of course it must be thoroughly understood that this is no more than a rough estimate, the, conditions of working and of buying horses are so different in different localities. It is extremely impropable that any machine can be constructed to take the place of horses for less than £500, but for the sake of argument we may admit that the cost of an engine and the cost of horses will be identical. The depreciation in the value of tram-car horses cannot be taken at less than 20 per cent per annum — will the loss of value in the case ol an engine be less ? This remains to be seen. If a satisfactory motor, say a steam engine, can be produced which will be as durable as a railway locomotive, and if a sufficient number of these motors be employed to work a line properly, then a decided saving may be effected by their use as compared with the expense of horse labour. Whether such an engine can or cannot be produced will not be known until engineers have tried to produce one ; and we are pleased that a fair prospect at last exists that the experiment will be made fully and fairly. In Copenhagen tram-cars have been worked for some time past with considerable success, and steam tram-cars are now running in Paris in a very satisfactory way. In this country the thing is being tested on an adequate scale with compressed air and also with steam.