over the coil, so as to embrace it as closely as possible without touching it.

As in the Siemens machine, the double pole of the upper bar is opposite in character to that of the lower one. Similarly also are the induced currents in the descending half of the revolving coil like in nature to the upper pole; while those in the ascending half follow the lower pole. Two brushes, tangent to a circular commutator, placed on the induction coil shaft, carry off the electricity in one continuous direction.

The machine shown in the drawings is the type "A" of 6000 candles illuminating power, and it is the one generally made use of in industrial works and other similar applications.

In France a number of industrial works, such as spinning and weaving mills, ironworks, open yards, and railway goods stations, have been lit up, each by a number of single-light Gramme machines. The result has been generally satisfactory; but the expense must be greater in each case than if the same number of lights were supplied from a single machine.

The Wilde Machine.-This must not be confounded with the machine first referred to under this name in the preceding chapter; where small steel permanent magnets with a Siemens armature revolving between them, passed

a current through electro-magnets to a second Siemens coil, and so to be utilized.

Wilde's "dynamo" machine (Plate I., Fig. 2) consists of two cast-iron circular frames, placed vertically and kept the requisite distance apart by stay rods. On the inside face of each disc, and consequently opposite to one another, are fastened at equal distances round each periphery the ends of sixteen round bar electro-magnets, which project out lengthways into the space between the circular frames; each set nearly closing up the space between the frames. In the central interval which is left, is placed vertically a round cast-iron disc, keyed upon a shaft running through bearings in the centre of each of the circular frames, and projecting beyond them, to carry the necessary driving pulleys, commutators, &c. Through this round rotating cast-iron disc are passed sixteen soft iron cores, projecting on either side of it up to the ends of the fixed electro-magnets already referred to, and corresponding in position upon the disc to theirs upon their respective frames. The portion of each core upon either side of the disc has its separate coil of wire upon it.

Thus upon each side of the rotating disc is a series of sixteen fixed electro-magnets, and of a similar number of revolving induction coils. The two halves into which the machine is thus divided may be kept perfectly distinct; a portion of the coils serving to react upon certain of the magnets, and to pass the augmented current on to the other portion, whence it is utilized in the manner required.

The Wallace-Farmer Machine.—This machine, known and used in the United States for some time back, is gradually coming into application in this country. It is shown in Plate I., Fig. 5. It presents, in appearance at least, some similarity to the Wilde machine. Upon its

central rotating cast-iron disc it carries, projecting on either side, twelve double coils; while the fixed electromagnets are but two in number, projecting from each endframe, somewhat as in the Gramme machine. The upper pair of electro-magnet bars have their opposite poles facing the central rotating coils; as have also the lower pair of electro-magnet bars, except that the pole exposed in the lower bar is the reverse of that in the upper bar immediately over it. By this arrangement the machine is practically a double one; each half with its commutator being capable of being used independently of the other.

The Brush Machine, though used in the United States, is not so far known in this country. It is the machine to which the committee of the Franklin Institute last year in their report "On Dynamo-electric Machines," after a lengthened series of experiments, gave the preference over the "Gramme" and the "Wallace-Farmer" machines. The diagram (Plate I., Fig. 4) is taken from the above report. The Brush machine is composed of a pair of fixed horseshoe electro-magnets placed with their like poles facing each other, with a circular armature rotating between them. This ring is not coiled continuously, as in the Gramme coil, but in portions, leaving alternate uncovered spaces between each segment, which are covered by iron extensions from the ring; as in the Pacinotti machine, to which it is said to bear some resemblance. The two upper electro-magnet bars have their like poles facing the central rotating coil; while in the lower bars they are also similar to one another but opposite in character to those of the upper bars; each pair of bars thus practically forms extended poles of opposite character.

The preceding "dynamo" machines may be classed as belonging to what is termed "single-light" machines ;

the sole utilization of the current generated being the production in actual practice of a single light. Although certain attempts, especially with the three last-named machines, have been made, and it is said with a fair amount of success, to support a series of lights from them, yet these trials can hardly be said to have passed into the domain of practical application.

The "dynamo" machines, which are about to be described, have fairly earned for themselves by actual and regular working for a long period the title of "manylight" machines. This is shared, however, also by the " magneto" machines of the Holmes-Alliance form, and by the De Meritens, their more compact successor. The distinguishing feature of the Lontin, and of the Gramme "many-light" machines, is that they are practically two machines; though perhaps under certain circumstances and with due proportions, the two might be combined upon one frame.

The Lontin Machine.-M. Lontin, unlike M. Jablochkoff and M. Gramme, each of whom attacked only a portion of the question of the divisibility of the light, has boldly faced the entire of the difficulty, including the lamps or regulators, and has offered a very satisfactory solution of each part of it. He has designed a special form of machine, or rather two distinct machines, to effect the object desired. In the first (marked A on Fig. 1, Plate II.), which may be termed the "generating" machine, the electric currents, feeble in intensity, are excited; they are passed off in one continuous direction to the second or " dividing " machine (marked B), which, after greatly augmenting their intensity, permits of their being collected from off its exterior casing, in a form divided and subdivided almost at will, and alternating in direction; this last being, in his