the plates must be quite long when the velocity is great. I employ plates two feet in length, and find that velocities from 16 to 40 inches per second give good results. The action of the light is however inversely as the velocity. To compensate for this, the size of the circular opening admitting the light may be increased. This, of course, causes an enlargement of the luminous image, and apparently involves an injurious widening of the line traced, but, as observed by Dr. Stein in his experiments, the effect of velocity is to narrow the line photographed, since the maximum exposure is in that diameter of the circular image which lies in the line of motion. This is a great advantage, since a variation of velocity in the vibration is marked by the widening of the line, often more clearly than by the form of the curve. I have employed the ordinary photographic process, not attempting to obtain special sensitiveness. The brightest sunlight is required, a slight haziness interfering seriously with the result. My heliostat employs two reflectors of ordinary looking-glass, and the loss of light is considerable. To guide those who may wish to try this method I add the following measurements: Diameter of circular opening Distance of mirror from circular opening.. inches.* -28 feet. Distance of mirror from photographic plate...11 inches. Focal length of lens... Size of steel mirror. 91 inches. .0.46x0.34 inches. The question naturally arises whether the mirror may not so interfere with the vibrating disc as to destroy its articulation. The telephone gives a direct answer and banishes the doubt. The mirror was attached in the manner already described to the disc of a telephone, and the instrument showed itself still perfectly capable of 'sending,' and 'receiving,' without noticeable loss of clearness or quality. Are all the audible elements of speech traceable in these records? in other words, is the record complete? I am not prepared as yet to answer this question definitely, but the following experiment leads me to doubt whether an affirmative answer can be given, while at the same time it illustrates in a striking manner the sensitiveness of the ear. The mirror was attached to the disc of a receiving telephone and a photograph taken from it while the instrument was talking audibly. resulting record was almost a smooth line, showing but very slight indications of movement of the mirror. It would therefore, appear that there are distinctly audible elements, which * Depending on velocity required, and on actinic intensity of the light. The are too minute to be recorded by this method. It is to be noted, however, that the width of the line traced where the vibrations are extremely small, is so great as to mask the curvature, so that the experiment just cited is not entirely fair. The clearness and beauty of the curves obtained can hardly be appreciated without inspection of the originals. Their complexity and variety open a large field for investigation, and they seem to offer the means of analysis of articulate speech. ART. VIII.-Suggestions for a Telephonic Relay; by Professor O. N. ROOD. AFTER reading an account of the experiments of Mr. Hughes,* which may be regarded as an extension of the work of Edison, it occurred to me that the peculiar property of carbon, upon which they depend, might be utilized in the construction of a telephonic relay. I accordingly arranged three pieces of carbon in the form of an H, attaching the two outside pieces to the diaphragm of an ordinary telephone; this, with a battery, was destined to act as relay and re-transmitter. The first circuit included, then, a common telephone as sender, and the coil of the relay; the second included battery, vibrating carbon, and a common telephone used as a receiver. It was found that the vibrations of the pivots of the central piece of carbon were indeed able to modulate an electric current, so as to reproduce with somewhat diminished intensity sounds uttered in the sending telephone. Eight small vibrating carbons were now substituted for the single piece, and the reproduction was effected without loss of intensity or distinctness. The battery used with the relay consisted of eight small cells of zinc and carbon placed in diluted sulphuric acid only. For a relay to be efficient it is of course necessary that it should increase the loudness of the sounds so as to allow for electrical re-transmission to a more distant station; this can probably be effected, 1st, by making the telephonic relay of such dimensions that six or eight carbons can be placed approximately over the center of the iron diaphragm, and 2d, by using simul. taneously several of these pieces of apparatus in the same circuit. An arrangement like Hughes's microphone was also employed as sending instrument; an inverted coverless cigar box was used, on which I placed three vibrating carbons instead of a single one. The multiplication of the carbons was due to a suggestion of Dr. W. Gibbs, who at the time proposed various * Nature, May 16, 1878. forms of sending apparatus, all including the principle of multiple vibrating points or surfaces of contact. This simple apparatus was very sensitive, and reproduced with fidelity conversation in a low tone at a distance of more than thirty-five feet from the box; its performance suggested to me the multiplication of the carbons on the relay. To the above I may add that when the electrical current used with the carbons is too powerful, a hissing, crackling sound is produced, which is from time to time varied by the introduction of a pure musical note, which often runs through considerable variation in pitch. This voltaic tone may be due to the repulsion exerted by the electrical current on itself, causing one of the carbon points to rise and fall with regularity in a manner analogous to the motion of the Trevelyan rocker, or it may be caused by rapid changes in temperature and hence in volume of the contact-surfaces. With fourteen small cups it occurred quite frequently. Columbia College, June 10, 1878. SCIENTIFIC INTELLIGENCE. I. CHEMISTRY AND PHYSICS. 1. On the Microphone of Hughes. At the meeting of the Royal Society on May 9th, Professor Huxley presented a paper by D. E. Hughes of London, on the action of sonorous vibrations in varying the force of an electric current.* The results described were obtained in an attempt to investigate, by means of the telephone, the effect of sound vibrations on the electrical behavior of matter. Using a Daniell battery of three cells, with a telephone in circuit, the wire conductor was subjected to strain until it broke; no sound was heard except at the instant of rupture. It was then noticed that the sound could be reproduced on making and breaking the circuit with the broken ends of the wires, or even more simply by connecting the wires with two nails placed side by side, a third lying upon them at right angles breaking or lessening contact whenever subjected to jar, even by sound waves. twenty nails piled up log-hut fashion, increased the effect, and a piece of steel watch chain worked very well. Still better results were obtained by the use of a metallic powder in a glass tube, the instrument in this form being so sensitive as to reproduce articu late speech. All finely divided conductors which do not readily oxidize, such as platinum, mercury and carbon, or still better metallized carbon (willow charcoal heated to whiteness and plunged into mercury) may be used for the purpose, a glass tube filled with such substances, and provided with wires for insertion in a * Engineering, xxv, 369, 384, May 10 and 17, 1878. Sci. Am. Suppl. v, 2024, June 8, 1878. Ten or circuit, being called a "transmitter." Exposed to sound, even when quite inaudible to the unaided ear, the resistance of the transmitter varies in consequence of the vibration, thus varying the current strength and producing in the telephone a distinct noise. The slightest touch on the table where it is lying, the merest contact with a feather or a camel's hair brush, is distinctly heard in the receiver, and both instrumental and vocal sounds are transmitted with power. Acting on these facts, Hughes devised an instrument especially adapted for magnifying weak sounds, to which he gave the name microphone. It consists simply of a piece of gas carbon, an inch long, inch wide at the center, and inch thick, pointed at the ends and supported vertically between two blocks of the same carbon which have small cavities hollowed out to receive it, the upper end being more blunt than the lower, and rounded. The weight of the upright piece is only just sufficient to make a feeble contact. With this form of transmitter the beating of the pulse, the tick of a watch, the tramp of a fly can thus be heard at least a hundred miles from the source of sound. In explanation of these facts, the author says: "It is quite evident that these effects are due to a difference of pressure at the different points of contact and that they are dependent for the perfection of action upon the number of these points of contact. They are not dependent upon any apparent difference in the bodies in contact but the same body in a state of minute subdivision is equally effective." The results which have been obtained by Hughes as above described, are clearly anticipated by more than a year by those of Edison.* In January, 1877, while engaged in perfecting an articulating telephone, Edison made use of the fact discovered by him in 1878, that semi-conductors have the peculiar property of varying their resistance with pressure. To the center of a diaphragm was attached a spring faced with platinum, in front of which, and movable by an adjusting screw, was a small cylinder of graphite. This arrangement gave great volume of sound but its articulation was poor. After extensive experimenting, using the graphite mixed with various substances, lead peroxide, copper iodide, pulverized gas retort carbon, manganese peroxide, amorphous phosphorus, finely divided metals, many sulphides, tufts of silk fiber coated with metals by chemical means and pressed into disks, etc., he was led to adopt a disk made of the lampblack from petroleum smoke and to use it in the primary circuit of a small induction coil. This constitutes the carbon telephone, which, certainly for long circuits is the loudest transmitter known. In June, 1877,† he described a new form of relay based on the principle of varying resistance by pressure, using disks of carbon on the poles of the receiving electro-magnet, on which disks the armature rested. The coils of this magnet were in the primary circuit, the cores, By *The Speaking Telephone, Talking Phonograph and other novelties. George B. Prescott. pp. 431, 8vo. New York, 1878. D. Appleton & Co. +Journal of the Telegraph, x, 163, June, 1877. |