Three-wheel vehicles have been used, but there is a difference of opinion as to their value, as the construction has disadvantages as well as advantages. It is evident that such a vehicle can be steered with greater ease than one running on four wheels, but on country roads, where the wagon wheels roll down a smooth surface, and leave the space between in a rough condition, it is equally evident that the third wheel, in passing over this uneven surface, would jolt the vehicle to a considerable extent. On a smooth pavement the three-wheel vehicle will run fully as well as the four-wheel; but, on the other hand, on such a pavement the latter can be steered with as little effort as the former, so that the question of superiority of design is one that probably depends upon individual taste. From the descriptions of automobiles given in this and the two preceding articles, it will be seen that although many of them are used, especially in France, they are not entirely free from objectionable features. The electrical vehicles are provided with the most simple and durable machinery, and, being noiseless, odorless and free from smoke, are all that could be desired in so far as their operation is concerned; but they are heavy and can only be used in places where the batteries can be recharged. The steam vehicles are light, have simple mechanism and can run anywhere; but they exhaust steam into the air, which is clearly visible in cold or wet weather, and the heat from the engine and boiler is an objection, at least in summer time. The gasoline vehicles run well, but are noisy, and the odor of the gasoline is disagreeable as well. SOME SCIENTIFIC PRINCIPLES OF WARFARE. BY WILLIAM J. ROE. As in boxing, fencing, saber and bayonet exercises, there are comparatively few postures, guards, thrusts and strokes, so in warfare, whether the numbers be large or small, the arms most modern or ancient, there are just a few principles to whose steady adherence and skilful manipulation all success is due. In order that these may become apparent without irksome study of military details, let us imagine a command of say a thousand men, fairly well drilled, of good ordinary intelligence and engaged in a cause worthy of being fought for. We have been in camp for some time, but an order has now come to join the main army. This is a long distance off, the railway communications have been broken, and the intervening country, though possessed of good roads, is more or less in the hands of the enemy.