THE TALKING LIGHT BEAM.

Star (Christchurch), Issue 7802, 5 September 1903, Page 2

THE TALKING LIGHT BEAM.

Tie Latest Thing ia tWlreloss Telephony. (By R. G. SKERRETT, In the New Orleans " Times Democrat.") The heliograph, which 'has blinked uncertainly its messages from crest to crest of mountain range, atid the searchlight that has winked laiboriously in the dots and \ dashes of the Morse code are to be put to another use, and in a, short while will be sending actual speech over many miles, by night and by dajy, with all of the facility and the accuracy of the common telephone. This wonder has Tjeen effected by the investigations and recent trials of Professor Ernest Ruhnier, of Berlin, and wireless telegraphy now has a very promising rival in th'B. wireless telephone. The nautical world especially is deeply interested. The German Government has appropriated 10/OOOdol for experimentation in the navy, and kaiser Wilhelm has directed Professor Runnier to cionducb an, exhaustive series of tests during the coming summer manoeuvres of the Baltic fleet. TEN MIIiES ON A LIGHT BAT. Already Professor Ruhiner has succeeded in telephoning distinctly over a distance of nearly ten miles, and: with the apparatus which- he is rapidly perfecting he expects to accomplish even greater things. The method employed is briefly this : —The current produced in the microphone circuit curren produced in the microphone circuit of an ordinary telephone transmitter is led into the current feeding an. arc lamp. These varying currents produce c corresponding variation in the temperature of the arc, and consequently alter the volume of the lamp flame. While these variations aie so slight that they cannot be detected by the naked eye, still they have been photographically recorded 'by the kinematograph. The light from the aarc lamp is thrown in jjarallel beams by means of a big iparabolic reflector upton 3 cell of selenium at a distant point. For this purpose the arc lamp and the reflector of a searchlight are found to answer best. At the receiving station there is another parobolio reflector, which, Hike that at the transmitting end, can be turned in any direction. In the centre, or what is termed the optical axis of the' receiving reflector, is placed a cylindrical cell of selenium, which, in turn, is connected with a battery and two telephone receivers. The , rays thus received act upon the selenium, which is very sensitive to the most delicate variations of light, and, trader this influence its electrical resistance alters, and a constantly changing current passes over the telephone circuit to the receivers of the telephone. In this way the speech at the sending station .is transmitted to th© receiving station, where the variable light waves are changed into sound waves and speech reproduced. NOT A NOVELTYWireless telephony is not a novelty in either principle or experimental performance; but for practical application on a promising commercial basis, the palm musb goto Professor Ruhmeiy However, America is not without its rightful claim to original achievement along this line, and to the unselfish work of Professor. Alexander Graham Bell, Professor Ruhroer is greatly indebted to-day, and he has acknowledged 1 it. In October of 1880, Professor Bell made Siblic the result of 'hjs labours in produc-. g and reproducing sound by light. He called his instrument the photopbone ; and his accoonplishments, while stopping upon the threshold of practical -usefulness, were quite, astounding,- and blajsed the way for the investigators that have since pursued j the subject. . TROFESSOB BTJHMER'S EXPERIMENTS. Professor Ruhmer in his efforts to make the Bell system a commercial success and of practical valae.. was aided by two ?ery important original discoveries. He found that selenium- is sensitive to other than the red and the yellow rays of the spectrum, as Jiitherto assumed t and he also d» covered that by increasing the size of iii-s mirror, which, was concave and not i plain, mi that of Professor Bell's photophone, he could increase the distance at I which the message would be audible. Pro- j fessor Ruhmer was also aided in 'his work j by the evolution of a type of selenium cell j that was wide in ats range of variability vi:der the action of light, and one, too, that recovered its normal resistance in <v very few moments after exposure to light. Some aotica of 'how the selenium cell ! varies" in resistance may be gathered from J the fact that a cell that had a resistance j of 120,000 ohms in the dark, When illuminated by only a sixteen candle-power lamp, quite near, fell to 1500 ohms— a ratio of 1 to 80. Professor Rrthmer, however, has made a type of cell recently that has a range (resistance varying from 1 to 200 from darkness to light ; and where his earlier cells, made a few months ago z required from ten to twelve hours to return to their original resistance after being subjected to intense illumination, his latest cells return to their original resistance in a few minutes. These cells are cylindrical in form, as in that fc J hape they can be placed in the focal line of th& mirror, and receive the light ur.dformly on all sides. Th«se cells are inclosed in an exhausted thin 'glass tube or globe, similar to the common incandescent house lamp, and are thus protected from at-mosphc-rie influences, especially dampness, to -which, tier ar-a extremely sensitive. The transmitting Tight consists of a searchlight supplied from batteries, for it has been found that the hum of neighbouring dynamos is distinctly reproduced at the other end. In fact, anything that would cause the light to flicker 'or vary would produce a correlative of sound at the receiving end, and, for that reason, the light must, of itself, 'be absolutely ate-ady. HOW THE MACHINE WOHKS. Now, lot iifis see how the thing works. If you will unscrew the flaring end of a telephone- receiver, you will find, first, a thin metallic <ike, and immediately under that two little magnets, which 2 under the varying impulses sent over the wire, cause the disc or diaphragm to vibrate and thus ti> produce sound or speech, as the case may be. The transmitter, in principle, is an exact duplicate of this mechanism, only it is connected with a small local battery; which sends forth an >eleci;rical impulse of changing dc-gr«e, depending upon the flexure of the disc in response to the range of tones of the voice. From the batteries feeding the searchlight is tapped a small wire leading to the telephone at the transmitting end. Ordinarily t no current could pa« through this conduit and back into the circuit before it reached iha searchlight ; but when the telephone transmitter is spoken into a way is opened-jj-thi* cur-

rent taking the place of the battery ordinarily connected with the transmitter— and tile total current finally fed to t.he light is made to vary slightly in sympathy with the impulse thus sent over the line. The result ia a variable intensity of light, but, as has been said, of so delicate, a nature that the eye unaided could not detect it. The" selenium cell, however, at the other end can. This cell, upon which the light is focussed from a big receiving concave mirror, responds to those very delicate shades, and in thus responding permits a current from local batteries to pasa on through its substance to the magnets and discs of two telephone receivers— thus enabling two per- | sons to hear the message at the same time. Ifc is all very beautiful and very simple in explanation, but the results would be more astounding could one only describe the many steps and the long, long hours of patient research and study that have led to these accomplishments. COW THIAIiS WEBB CONDUCTED. 4 Professor Ruhmer conducted most of hi* trials on the Wansee — the experiments being made both by night and by day. In the daytime the professor succeeded, provided the sun did not shine directly into the mirror at the receiving station ; and to obviate that a screen was devised that worked admirably. The prime difficulty to be overcome in effective work is that of getting the positive crater of the light in perfect focus with the big parabolic trartsmittins; mirror, and then in bringing the beam of light directly upon the projector afc the ' receiving station. This is not easy to arrange, especially from a movable point, such as a ship. To orercome this, the professor will use a telescope in combination with the transmitting reflector, so that th« optical axis of the two instruments may 'be adjusted 1 in par* alkl. The professor says : " Although experiments were made on the Wansee and the Navel in the evenin?, when there is nearly always a mist on the surface of the water — in fact, in one experiment rain was falling — the conversation could always be undtntood." . MORE WONDERS TO COMB. Of course, these accomplisrhmenfs are but the beginning of more startling achievements, and Professor Bell said recently that the only limit to this method of speech transmission would be that occasioned by the curvature of the earth. As far as the light could be seen the telephone could be used without wires. Thera are other adyantages besides the wirelessness of this system. Messages can be sent more rapidly than by telegraph and with greater accuracy, the replies can be despatched back instantaneously, and, what is even more vital, perfect secrecy can be assured. Even if Professor Ruhmer should not increase his present record of transmission, over nearly ten miles, the system would be of incalculable Talue for communication between ships on the high seas and {or direct communication between ships approaching one another in thick or foggy weather while under way in any waters.