ments cost the Emperor Nicholas at least 60,000 franes.

Davidson's Motor.-The motor which Mr. Davidson applied to his locomotive is represented in Fig. 32, for which cut we are indebted to the Electrician'; and as will be seen, it consisted of two cylinders of wood fitted to the axles of four wheels and furnished with four sets of iron armatures arranged so as to turn between the poles of eight electro-magnets. These were fixed horizontally at the bottom of the carriage, and were arranged two and two by their opposite poles in two parallel rows, so that each cylinder carried two sets of iron bars parallel to the axles, and presented themselves successively during the rotation of the cylinders to the poles of the corresponding opposite electro-magnets; so that when one of the bars on one side was opposite its electro-magnet, one on the other side was just within range of the attraction of its electro-magnet, and vice versa. In this arrangement, if the current was interrupted in the active electro-magnet and sent into the one on the other side, the movement once started continued, and produced a rotary movement in the axle. Each of the four sets of armatures produced the same effect, and added together, developed sufficient power to turn the wheels of the locomotive. The commutators for making and breaking the current were little different from those used at the present day, only Davidson employed two batteries in troughs placed one at each end of the carriage, one acting on the electro-magnets on the right, and one on

those on the left. For this the axles carried at each end two small metal cylinders, on which pressed the brushes in connection with one of the batteries and the electro-magnets belonging to the one set. These cylinders were composed of two parts—one plain, and one with a number of grooves corresponding in number with the armatures; and these grooves were filled with ivory. The current from the battery arrived at one of the cylinders by the rubber pressing on the plain part, then passed from there by the metallic parts of the cylinder to the electro-magnets of the right or the left as the case might be, and thence to the battery; but as, in consequence of the movement produced by this current, one of the ivory parts was brought under the brush, the current was broken in the electro-magnetic system which had produced the movement, and not being held back by the attraction of the armatures, the cylinder continued its movement by virtue of the acquired velocity, and the action going on at the other end of the axle. The position of this commutator was in fact such, that when one ivory part was under the brush of the first commutator a metal part was under the second, and caused the current to flow from the second battery through the second system of electro-magnets.

The batteries employed by Davidson were those of Sturgeon, composed of plates of iron and amalgamated zinc measuring 15 inches by 12; each was divided into two parts, so that each set of magnets had its own battery; there were 40 elements arranged in

the same way as Wollaston's trough battery. This battery could also be reinforced by a spare battery of 19 cells fitted on the platform of the carriage, which was 16 feet in length, 6 in breadth, and weighed 5 tons, including the batteries and the mechanism. The speed attained was said to be four miles an hour. Engineers estimated the power thus developed on a line of rails at less than a horse-power, but the author of the letter whence these particulars are obtained believes that the power developed was much greater.

The electro-magnets employed by Davidson were made of plates of iron bound together; each of the arms was 25 inches in length, and the rectangular poles were 8 inches by 5, and were only 4 inches apart. The magnetising coils were composed of bundles of cotton-covered wire. At first the magnetic poles were almost in contact with the armatures as they passed before them, but the enormous attraction in a straight line which was then developed and which bent the supports, necessitated the separation of the parts, which of course produced a diminution of the power developed; and this circumstance somewhat discouraged the inventor.

Wheatstone's Motors.-The conceptions of this inventor being always remarkable for their ingenuity, we must describe the different models mentioned in his patent of the 7th of July, 1841, and as we shall have occasion presently to describe that already referred to, which figured at the recent Electrical Exhibition in Paris, we shall only now

describe those shown in Figs. 7, 8, 9, and 10 of his patent.

In one of these motors the magnets consisted of teeth set widely apart on a large iron wheel round which were wound the magnetising coils, and the connections of these with the battery were so arranged that contrary poles were alternately presented. There were 24 of these coils, and each pair formed a two-armed electro-magnet, and the wheel was fixed in a vertical position. On the conical surface formed by the iron teeth acting as electromagnets, was a circular crown of iron, belonging to a wheel whose axis was carried at one end by a vertical ball and socket movement, and at the other by a crank on a flywheel shaft, the latter carrying also a pulley and commutator with twelve insulated contact pieces. This commutator, by means of rubbing springs, sent the current from one electromagnet into the following, as the iron wheel revolved round the circle of electro-magnets, and this rotation resulted from the movable wheel passing from one electro-magnet to another taking different positions on account of its axis being fixed at one end, thus imparting circular movement to the crank to which it was fixed at the other.

The second motor consisted of six straight electromagnets so arranged as to form the sides of a hexagon, without, however, their poles being in contact. This hexagon was fixed in a vertical position, and parallel to it a movable plate fitted with three horse-shoe permanent magnets, so arranged