(Here we have transformed a sound which in the first place gave out no visible movement, and which might from this be supposed to be due to some molecular motions, into one of direct mechanical movement recognisable by touch, and where molecular action is not at all necessary to its explanation.)

XXIV.-Knowing that each diaphragm in a telephone has its own dominant tone, which accompanies all sounds emitted, the diaphragm was divided into two slightly unequal portions. Clear loud tones were then produced as before, but they were accompanied with two dominant tones-in fact, a chord, due to the different dominant tones of each segment of diaphragm. By chance they happened to be an exact fifth, and the word "telephone," like all other words transmitted to it, was accompanied by the dominant chord, thus:

and I am convinced that by proper arrangements four segments reproducing the whole cord could have been obtained, thus:

(To be continued.)

THE WERDERMANN ELECTRIC LIGHT.

THE most recent development of the electric lighting system is that invented by Mr. Richard Werdermann, and which was shown on Saturday, November 2nd, at the works of the British Telegraph Manufactory, 374, Euston Road, to a number of scientific gentlemen and representatives of the press.

Mr. Werdermann was assisted in his experiments by Mr. Berger Spence and Dr. Cornelius Herz. The chief object of the inventor was to demonstrate that by the new system a considerable number of lights could be placed in one circuit and steadily maintained without the employment of any clockwork or electro-magnetic apparatus connected to the lamps.

The display was chiefly of an experimental character, the lamps used being somewhat different in construction to those which will be placed in actual work, but it was quite sufficient for scientific purposes.

The principle of Mr. Werdermann's invention, consists in keeping a small vertical pencil of carbon in contact with a large horizontal disc of the same material above it. Mr. Werdermann was led

to adopt this arrangement as the result of numerous experiments.

Referring to fig. 1, which shows the ordinary arrangement of carbons in an electric lamp, it is well known that when the passage of the current is such that the top carbon is a positive pole, the end of this carbon becomes cup-shaped, whilst the end of the other carbon becomes pointed, by the action of the current. By increasing the lower carbon considerably in sectional area, Mr. Werdermann found that, with the same amount of current passing, it was necessary in order to maintain the continuity of the arc, to place the two carbons closer together; he also noticed (as a curious fact) that a little cylindrical pimple of carbon was formed in the middle of the lower carbon electrode, as shown by the figure; also the end of the upper carbon tended to spread out. On still further increasing the size of the lower electrode, it was found necessary to bring the two carbons still closer together in order to maintain the continuity of the arc; the little cylindrical pimple then became much smaller in size, and the end of the upper carbon spread out still more. If now, the lower carbon was still further enlarged, so that it had a sectional area sixty-four times as large as that of the upper carbon, it was found that the continuity of the circuit could only be maintained by keeping the two carbons in actual contact; and further, it was observed, that the end of the upper carbon, which had previously tended to spread out, now took a pointed form. When actual contact took place the little pimple of carbon disappeared, and a brilliant light was given out by the incandescent point.

Figs. 5, 6, and 7 show what occurred when the larger carbon formed the positive pole. Under these conditions the end of the small electrode became heated to a red heat only, whilst a small portion only of the large electrode became heated to a white heat by the passage of the current; this was also the case when the upper electrode was increased in size, and the two carbons had to be approached closer together in order to maintain the arc. When, however, the upper carbon was increased to such a size that continuity could only be maintained by actual contact, then a curious change took place: the upper carbon no longer glowed, but the point of the smaller carbon, previously only red-hot, now became white-hot, and assumed the conditions shown by fig. 4. The light given out when the larger carbon formed the positive pole was found to be not quite so great as when it formed the negative pole. The heat being almost entirely confined to the smaller carbon, the larger one was not consumed to any appreciable extent.

During the whole time that the smaller carbon burns, it retains its pointed form, and a small electric arc is plainly visible round the points of contact of the two carbons. The greater part of the light given out is produced by this small arc.

In accordance with the foregoing results Mr. Werdermann constructs his lamps in the following

manner :

He places the negative electrode uppermost, giv ing it the form of a solid disc of carbon, about two inches in diameter and one inch thick. This is encircled by a band of copper ribbon and prolonged to a terminal to which one of the machine wires is attached. The lower or positive carbon, which is a

thin round pencil, 3 millimetres in diameter, is placed vertically beneath the negative electrode, in a tube up which it slides. This tube has a prolongation of thick copper divided in two parts, and pressing against the pencil and forming contact with it, this forms the other terminal of the lamp.

The lower carbon is kept in contact with the upper one by chains attached to its lower extremity, coming up over pulleys and down again to a counterbalance weight, which always keeps the point of the pencil in gentle contact with the disc as the former gradually burns away.

By referring to the sketch, fig. 1A, the general idea of the lamp will be seen at a glance.

"a" is the negative carbon, b is the pencil sliding in the tube c, and gripped at the top of the tube by the split contact piece, the pressure of which is regulated by the spring d. The conductors e form part of the lamp post, having terminals at the bottom, and one is connected to the tube, the other, by means of the semicircular piece of metal f, to the upper carbon; fis hinged for the purpose of moving away the negative disc when a globe is to be put on the lamp.

The tube is shown in perspective for the sake of greater clearness.

The experiments were commenced by putting two tall lamps in circuit such as will be used for out-door lighting.

These lamps gave a light estimated at 360 candles each, and were connected together in parallel circuit. The lamps had no globes, and the lights were wonderfully clear, of a pure colour, and perfectly free from the blue or purple rays so often seen in the electric arc. Better than all was the remarkable steadiness of burning, there being an entire absence of any jumping or flickering whatever.

After allowing these to burn for some time, the current was then sent through a row of 10 smaller lamps, arranged on a shelf, and connected parallel. These lamps were estimated to give about 40 candles each, each one burned with the same brilliancy and steadiness, and proved most conclusively that the divisibility of the light was an accomplished fact, and when we say that this satisfactory result was obtained with an electro-plating Gramme, the bobbins of which are wound with thick copper ribbon, and giving an electro-motive force of only 4 Daniell's cells, it seems probable and reasonable to suppose that with suitable machines, Mr. Werdermann will be enabled to put 50, 100, or even 500 lights in circuit, and thus solve the problem of dividing the light more completely than has hitherto been the case.

In fact, Mr. Werdermann stated that had his lamps been ready he could have put in circuit a considerably greater number of lights than were exhibited.

Fig. 2A shows the connections of the 10 lamps. The thick wires + and are the cables connecting the lamps with the Gramme machine, the first lamp on the pos. being the last on the neg. The spirals "a" are equal resistances placed in the circuit of each lamp for the purpose of rendering any variation in the contact or pressure of the two carbons less appreciable to the passage of the divided currents.

The resistance on the average of each small lamp including the extra resistance "a" is o'392 ohms.

5 lights parallel

,, 0'076 ohms. 10 lights, do., as exhibited 0'037 ohms. The resistance of the large lamps is rather less than that of the small ones.

In the 10 small lamps the carbon pencils burn away at the rate of about 2 inches per hour.

The large lamps having pencils of 4 mm. diameter, burn from 2 to 3 in. per hour.

The carbons are manufactured in Paris in lengths of about one yard, and at a cost of about 1 franc per yard, which length would keep up a light for 12 hours.

The negative discs are of ordinary battery carbon, and the weight required to keep carbons in contact is about 1 lbs.

The length of carbon protruding from the tube and made incandescent is of an inch, but this length can be varied at pleasure. However many lights may be put in circuit the extinction of one or more will not affect the rest, a switch arrangement attached to each lamp effecting all that is required for the regulation of the current.

Then again, by this system, all the lamps are lighted simultaneously, and can all be as readily extinguished, and again re-lighted.

In regard to the strength of this light, we have before observed that one object of the inventor is to moderate the intensity, so as to avoid having any of the illuminating power reduced by covering the

electro-motive force of the current to the pressure of gas.

For instance, if a gas-holder held sufficient gas, and had enough pressure to supply 100 burners, it would be necessary to increase the quantity and pressure of the gas to equally light 200 jets. It is the same with the electric light. If with one machine of given quantity and electro-motive force, 100 lights can be produced, then if 200 lights are required we must have a machine with a greater quantity of current (corresponding to the capacity of the gas-holder), and with greater electro-motive force to carry the lights further away (answering to the pressure of gas).

In conclusion we give some details of the machine by which the lights were produced. It is of the old form of Gramme electro-plating machine, with four upright electro-magnets, and two bobbins revolving between them. The bobbins are iron rings wound each with 48 sections of copper ribbon sevensixteenths of an inch wide, and one-tenth of an inch thick. Each section has three convolutions. One bobbin is used for magnetising, or feeding the electro-magnets, the other for producing the working current. The resistance of this latter bobbin is about 0.008 ohms, and the electro-motive force, as before mentioned, is only four Daniell's cells, the machine being driven at a rate of about 800 revo

ееее

Each division in this circle corresponds to a motion of the fifty-thousandth part of an inch imparted to the vulcanite strip, and thus a corresponding small degree of pressure can be brought to bear upon the carbon button below the strip. A polished cone converges radiation upon the vulcanite, which is enclosed in a metal casing except on the side opening to the cone. The upper and lower faces of the carbon button are in metallic communication with a cell or two of a constant voltaic battery and with a delicate reflecting galvanometer of low resistance. A Wheatstone's bridge and resistance coils are also included in the circuit to balance the resistance of the carbon; and at first a "shunt" of thick wire is necessary to deviate through itself the greater part of the current, and so curb the motions of the galvanometer needle. When the proper balance is obtained-the fine adjustment being made by turning the micrometer screw that presses the carbon--the shunt is removed and the tasimeter is ready for a test experiment.

The heat radiated from one finger held near the cone is more than sufficient to drive the galvanometer index right across and off the scale. In a letter relating to this tasimeter, Mr. Edison writes to me as follows:-"By holding a lighted cigar several feet away I have thrown the light right off the scale," and by increasing the delicacy of the galvanometer, "the tasimeter may be made so sensitive that the heat from your body, while standing 8 ft. from and in a line with the cone, will throw the light off the scale, and the radiation from a gas jet 100 ft. away gives a sensible deflection."

These statements-less extravagant than those that have appeared in some newspaper reports-are quite consistent with my experience of the instrument, and they show that the tasimeter is a marvellously delicate thermoscope, and as such, or as a means of detecting minute variations in pressure, it is a really valuable addition to the cabinet of the physicist. It is not, however, likely to displace the thermo-electric pile in experiments on radiant heat; albeit, when the small area on which the radiation falls in the tasimeter is taken into account, it is no doubt a more delicate thermoscope. In fine, owing to the narrow linear surface it exposes, the tasimeter will probably do good service in such researches as the distribution of heat in solar and other spectra, and in exploring the ultra-red portion of the solar spectrum. By an ingenious device, characteristic of the man, Mr. Edison has shown how the tasimeter may be used as an instrument for detecting the presence of moisture in the atmosphere. All that is necessary is to remove the vulcanite strip and replace it by a strip of gelatine varnished on the unexposed side, when it becomes an hygrometer of surpassing delicacy. Another application of the tasimeter, which, perhaps, Mr. Edison will allow me to suggest, is for detecting variations in the pressure of the atmosphere. As a new form of aneroid baroscope it would doubtless give extremely prompt and delicate indications, and thus be of considerable service to meteorologists. The application of the instrument for detecting minute changes in the length of a body is obvious, but before it can come into use in any quantitative experiments, further investigation is necessary, and several minor modifications of the present apparatus are requisite.

Notes.

THE TELEPHONE.-Mr. McLure, the manager of the Bell Telephone Company, London, has effected several convenient improvements in the Bell telephone, and its fittings. To adapt the telephone for general household use Mr. McLure arranges an alarm bell, indicator, and commutator in the servants' hall, and a telephone in each room. When a person in one of the rooms wishes to communicate with the attendant he simply touches a spring in the stem of the telephone at his disposal: this rings the alarm bell and indicates the room from which the call has come to the attendant. The attendant, by setting the commutator to that room, re-sets the indicator to its zero position and puts his telephone in circuit with that in the room in question. Conversation can then be carried on between them. By this arrangement telephones can be supplied to every room in a house at as cheap a rate as electric bells, thus effecting a considerable saving of time and trouble. By a similar arrangement persons in different parts of a city can converse through the medium of a central station, in which the commutator is placed. Mr. McLure, among others, is now experimenting with a view to overcoming the induction clamour on tele. phone lines.

THE MICROPHONE.-On another page we publish an important investigation by Professor Hughes into the sources of sound in the telephone-a problem which has been rendered soluble by means of the microphone. The research in question is the continuation of some former experiments recorded in the Telegraphic Journal for September 1. Some of the facts demonstrated cannot fail to be useful in the improvement of tele. phones.

THE PHONOGRAPH.- The Stereoscopic Company are not yet prepared to supply phonographs to purchasers. The price to be put on them when they are offered for sale is, we believe, thirty guineas.

THE ELECTRIC LIGHT.-The details of Edison's new invention are still kept secret, and, as will be seen from our list, a second patent has been applied for. Meanwhile, the Scientific American professes to give the following partial information, which is a little more explicit than what was vouchsafed to us in our last issue:-"The Edison light," says our contemporary, "is based on the well known fact that a wire may be heated by an electric current, the basis of many attempts to accomplish what Mr. Edison claims to have done. The reader may have seen the gas jets of the dome of the Capitol at Washington, lighted by similar means. Over each burner is placed a coil of platinum wire, which, when heated by the electric current, ignites the gas. Mr. Edison uses the coil itself as the source of light, the current sent through it being strong enough to make the coil white hot, or self luminous. The difficulty to be overcome at this point was the liability of the wire to fuse and spoil the light; a difficulty which Mr. Edison claims to have obviated by the introduction of a simple device which, by the expansion of a small bar the instant the heat of the coil approaches the fusing point of platinum, interposes a check to the flow of the current through the coil. This automatic arrangement, in connection with an auxiliary resistance coil, secures, it is said, an even flow of electricity through the coil, and consequently a steady glow of pure light. If this is done economically it is obvious that a marked advance has been made in artificial illumination." It may be presumed that Mr. Edison