Show s il vv THE RHE 7 as 1 9 as af T aej I 1 space el bys Meana nabil I 1 1 1 1 A wonderful invention tion 7 or of boals A on 0 PM reit defa the ir I t worked beirs adio by w aich conver conter transmitted th rough space o on n WAY a majl af or electricity f bene I 1 in hion of th e ap pari J agns bisone isone ane of the scientific wonders at we T by i W haw a telephone ul ephon e is caused to respond to the var radiations lations in jn intensity of W a tian upon a selenium c elcya el ip a L loo loos local s electric circuit c re u it is familari famiS ari prat alexander graham dell bell in transmitting articulate a to speech ln in this way by malting making a beam of light which iii a mirror reflects vibrate the vibrations beings being of the si sane niIna atina a ag 4 those produced by speak iiii ix through a membrane he used a thin tb mica duglass or glass plate as a diaphragm which aich by being silvered served at the kaaa te time as a mirror the reflected of light as it fell upon the selenium it the distant point varied in intensity in i unison with the sound waves wave s which caused the vibration of the atia diaphragm mirror the varying intensity of 0 chri light produces in the selenium cell a corresponding correspond ing variation in the resistance of the local circuit and the varying current which results is translated into sound waves ei by the telephone which correspond exactly with the sound waves which vibrated the diaphragm prof bell pursued his hip investigations looking to obtaining sounds without the addition of a local cl circuit auit and his latent production that which ls is now naw about ready for exhibition in the bell telephone pavilion in electricity building may be briefly described its as foli lows in the northwest gallery over hanging the main floor a few feet there has been erected a small platform upon which the sending apparatus is ib placed this consists of a focusing are lamp of ordinary pattern w whose hose rays rendered parallel by a lens are reflected from a thin diaphragm bragin mirror to the receiving instrument about eighty or ninety feet away at the north front of the thedell bell tei telephone ephone pavilion the reflect reflecting ine mirror is a all s very thin glass r silvered il vered on its reverse side adix hela helstin s heavy VY brass frame by means of washers of ordinary alt eting paper opening into the chamber in the rear of this mirror is an ordinary speaking tube into which W aich the sounds are uttered causing the mirror mirro r to vibrate as would the diaphragm of a telephone transmitter these rays reflected in par parallel lines are received at the farther end by a parabolic reflector in the focus of which is placed a glass bulb containing a small portion of ordinary burnt cork the bulb is blown into the end of f a glass tube about a quarter of an inch in diameter and four inches long the other end of which is open and to which is attached an ordinary phonograph hearing tube which extends into a small cabinet where the listener removed from external noises receives the message the only adjustments required are that the rays be directed from the mirror in the gallery in in an axial direction into the parabolic reflector and that the bulb containing the burnt cork be brought to the focus of the parabolic mirror this latter is accomplished by pushing the glass tube in or out until satisfactory results are obtained certainly nothing cou could id be simpler than this but although the instrument is of great scientific interest it has no apparent practical value the transmitted words as heard through the hearing tubes lack sharpness of definition and have a somewhat muffled sound which is ia probably due to tad the tube effects the conversation can however be fairly understood if one knows beforehand what is to be expected but it would be difficult to follow an expression for which one was not prepared prof bell has given the following explanation of the philosophy of the phenomenon when the intermittent beam strikes upon upon the receiver the particles are alternately heated and cooled when w ben they are heated hea ed they elpa expand n d and consequently the intervals which chic h are filled with air i are diminished when the light is intercepted the particles are cooled and the spaces between them enlarged air is squeezed out from the interstices between tw een the particles in the first case and nd drawn in in the latter the enlarging of f the intervals causes refraction of the air in the cork particles and the outer air rushes in the contraction of the interstitial spaces space s causes condensation densa tion and escape of the air they contain these two effects are still further increased by the heating and cooling of the air in the intervals alternately increased and diminished by these means alternate waves of compression and rarefaction are produced in the surrounding air and it is to this that the sound which is emitted owes its existence |