"I took a turned iron ring furnished with sixteen equal teeth. This ring was suspended by four brass arms BB (Fig. 44), which fixed it to the axis of the machine. Between these teeth little triangular pieces of wood were let in, wound with silk-covered copper wire. This arrangement was to obtain perfect insulation of the coils or bobbins thus formed between the iron teeth. In all the bobbins the wire

was wound in the same direction, and each was formed of nine turns. Each is thus separated from the other by an iron tooth and the triangular piece of wood. On leaving one bobbin to commence the next, I end the wire by fixing it to the piece of wood which separates the two bobbins. On the axle carrying the wheel thus constructed I grouped all the wires, of which one end formed the end of one

bobbin and the other the commencement of the next, passing them through holes for this purpose in a wooden collar fixed on this same axle and thence attaching them to a commutator also on the axle.

"This commutator consisted of a ring or small cylinder of wood, having on the circumference two rows of grooves, in which are fitted sixteen pieces of brass (eight in each row); they are placed alternately, and concentric with the wooden cylinder on which they form a spindle. Each of these pieces of brass is soldered to the two ends of wire corresponding with two following bobbins; so that all the bobbins are connected, each being joined to the following by a conductor, of which one of the pieces of brass of the commutator forms a part. If we put two of these pieces of brass in communication with the poles of a battery by means of two metallic rollers G, the current, in dividing, will go through the coil at both points where the ends of the wire fastened to the pieces of brass communicate with the rollers; and magnetic poles will appear in the iron circle in the diameter perpendicular to A A'. On these poles acts a fixed electro-magnet, which determines the rotation of the circular electro-magnet; the poles of the circular electro-magnet when in movement always appearing in the fixed positions corresponding to the communication with the battery.”

This machine is particularly worthy of notice, as it may be considered a veritable Gramme induction machine, and Pacinotti from the first so well understood its capabilities, that he described it in his

'Mémoire' as follows:- "It seems to me that what increases the value of this model is its faculty for being transformed from electro-magnetic into magnetoelectric with continuous current. If, instead of the electro-magnet, there was a permanent magnet, and the circular magnet was made to turn, we should have, in fact, a magneto-electric machine which would give a continuous induced current always in the same direction. To develop an induced current by the machine thus constructed, I brought to the magnetic wheel the opposite poles of two permanent magnets, or I magnetised by means of a current the fixed electro-magnet, and I made the circular electro-magnet to turn on its axis. In both cases I obtained an induced current always in the same direction. It will easily be seen that the second method is not practicable, but that an electro-magnet is easily replaced by a permanent magnet; the electro-magnetic machine resulting from this will have the advantage of giving additional induced currents all in the same direction, without necessitating the use of mechanism to separate the opposite currents or make them converge.'

6

Pacinotti closes his Mémoire' with this interesting remark, which seems to be the first indication of the reversibility of electric motors: "This model," he "further shows how the electro-magnetic says, machine is the complement of the magneto-electric machine, for, in the first, the current obtained from any source of electricity circulating in the bobbins produces movement of the wheel with its consequent

mechanical work; whilst in the second, mechanical work is employed to turn the wheel and obtain, by the action of the permanent magnet, a current which may be transmitted by conductors to any required point."

The Pacinotti machine remained for a long time forgotten in the Philosophical Museum of the University of Pisa, and it was only when the Gramme machine made its appearance, in 1871, that that of the learned Italian was recollected and brought before the public. It was sent to the Vienna Exhibition of 1875, and every one will have seen it at the Paris Electrical Exhibition of 1881, where it attracted great attention from those interested. We have dwelt much upon this machine, for it was with Gramme machines that the first experiments were made in 1873 with respect to the reversibility of dynamos, which have led to our knowledge of the transmission of power and all the attendant interesting results which have attracted the admiration of electricians of the present time: which results we will more fully consider in the second part of this work.

G

CHAPTER III.

EARLY ELECTROMOTORS.

IN the preceding chapter we have described in the order of their date the arrangement of the primitive electromotors, and have specified their particular characteristics. But as, since the year 1844, inventions have succeeded each other with great rapidity and have become extremely numerous, we have thought it better for clearness of description to abandon the chronological order and consider the apparatus in different classes, grouping together those founded on the same principle. Looking at the question thus, we find that all the systems, until the time when it became really an industry, may be classed under four heads, viz.: 1. Electromotors founded on the dynamic properties of currents; 2. Electromotors founded on the attraction of iron to electro-magnets, and on the properties of electromagnets; 3. Electromotors in which the attraction of gravity is introduced as a source of power: 4. Electro-chemical motors.

1.-ELECTROMOTORS FOUNDED ON THE DYNAMIC PROPERTIES OF CURRENTS.

Barlow's wheel, Faraday's tourniquets, Zamboni's dry-pile application, and a number of other instru