Show RECENT SCIENTIFIC DISCOVERIES DICOV Note These papers on Practical Sd Science ence nce have haye been prepared for The Her Heralds Heralds aids Home Hore Study Circle by Professor Wilam William J Hopkins of Drexel Institute IL IT S TELEGRAPHY Continued The T Work of Hertz Hez The Te idea of the electromagnetic char character character acter acte of light was wa advanced by Clerk Maxwell lawell about 1864 and the he theory thery was fully ful developed in his book published In 1873 The Identity in character of alt all al other lather waves wave was wa generally accepted as asa asa a fact fat before it ft was wa demonstrated ex cx experimentally and many may investigators Or 00 TO Hertz Hez Oscillator had worked in this fis direction in vain yain be before before before fore the solution of the problem was hit upon by b Hertz Herz It I is easy to start waves wave in the ether etherI In fact almost any ay natural phenomenon starts start them them The Te difficulty was in de detecting their presence prence when they lay outside the range rge of light and heat effects Rapid Discharges Oscillatory When an electrically charged body bod is Ic i discharged the character of the dis discharge discharge charge depends upon uvon the properties of the discharging circuit If I that circuit i has ha magnetic tc properties in any ay marked degree mag it acts act as a damper aper anti and ad the charge runs off of with wih comparative comparte slow slowness slowness slowness ness as a a current In one direction only If I however the magnetic properties are ae absent or of very small manE value the elec trio trie charge chae surges rapidly out out past pat the point of equilibrium then back again agin and oscillates in this way until the energy has h been dissipated as heat beat heat A spark discharge of which lightning is isan s san an anex example mple on the greatest scale known to us oscillates mates willie while it lasts last at the rate rte of perhaps many m million times a sec second sec second ond and starts waves wave in the tle ether et cr of oCa a corresponding sr frequency and ad length The rate te of oscillation depends upon the properties of the discharging circuit and by a proper adjustment of that circuit the length of wave wava may my be regis regu regulated reg late The oscillatory character charter of such sch a ai i I discharge was known know many ma years be he bel beI l I fre Hertz but as no method was known kown of detecting such ether waves in space the te experimental investigation of their properties was impossible Hertz discovered a method of detecting these thee waves and ad armed ared with wih this de tie detection he pushed through a rapid and ad adi i thorough series seres of experiments experiment which i placed place this branch of science at once I on cn a sound soud basis of fact p Detector It was while experimenting with a apr pair of similar coils cois of wire wre intended to show pr induction effects that hat Hertz no noticed noticed noticed that if a small smal Leyden Le den jar or small induction coil coll coi was discharged through one oe of the coils cois current could be induced in the other provided the circuits were not complete There must be b a short This in jn the first firt coil coll coi furnished the te means for exciting the very ve sudden disturbance of the te ether and the second coil ci sim aim similarly arranged arged became a detector of ether eter waves ves responding most mot strongly to ether vibrations of its it own natural period In all al his experiments Hertz made use of sympathetic or resonating ac action acton flea tion ton The exciter was the spark pass passing ing lag between two polished balls bals on either side of the break in the discharging circuit cruIt which was fed by the action of ofa an a ordinary ordina coil coi The de tie detector detector or electrical eye as a Lord Kelvin has called cale it it was wa usually a simple rectangle or circle of zinc zinc In Inthis Inthis Inthis this wire wre there ther was a break brea with wIt a akob knob kob or ball bl on each side and ad the dis distan tan e between the knob could be reg regulated regulated abated by a micrometer screw Although I this detector would respond within a considerable range the sparks reached reache i ia a maximum for a particular adjustment I at at which the natural periods peros of the ex exciter e exciter I citer and the detector were the same sae An improvement made by b later investigators investigators consists in keeping the spark terminals immersed in oil oU This pre prevents prevents vents ent the roughening of the surface and seems seem to make mae the discharge more regular probably by hy the same action te an anas as that of the te electrolytic interruption Properties Pope of Ether r Waves Waves By means mean of these thee simple devices deice Hertz made a a complete Investigation of at the te properties of electric waves in inthe inthe inthe the ether etler et er He found that tat they were reflected by metallic surfaces but passed through wood and stone and pase other oter insulating substances substance and ad he succeeded in refracting them the by a great geat prism of or pitch just as a light is refracted by a prism of glass gl s He measured the length lengh of waves aves and anti their speed S pe which was the same e as that of light In the course coure of a lecture l tte delivered not long after this Lodge said sd referring to ether ta waves of ot thIs kind kId They can be re reflected re reflected feted by plane sheets sheet of metal matal con concentrated on by parabolic reflectors reflector re refracted re no by prisms concentrated by lenses lenses I have hae at the college a large la lens len of ot pitch weighing over ove three hun hundredweight hundredweight for concentrating them theta to toa toa toa a focus They can c be bade made to show tha the phenomena of interference and ad thus thu have their wave waye lengths accurately measured They The are ae stopped by all 31 con conductors conductors I due tors and transmitted by all al insulators Insulators Insulators I Metals are opaque but even Imperfect insulators such as wood woo or I stone are strikingly transparent and waves wave may be received in one room rom from a source soure in another the door dor be between between tween the two being beig shut Space Telegraphy This was wa the germ of ot space teeg phy ph in its it present form for Th The wave is i started by suitable apparatus travels traveis trave through the te ether with wih the speed of o light and Is received by other devices much more mor sensitive than than that that used by bj Hertz These will wi be described later laler An Aa the ether waves are absorbed by conductors cond the action in the usual method of ot signaling with wires wIre is i evi evidently e 1 dently denty only a special case ease in which the toe ether waves started at the trans f PIRK r r 4 Hertz Hert Detector end are ae received r by y the wire o othe of the circuit the disturbance penetrating the wire from rom the outside and in this thi way a much larger proportion of the I energy is used where w ere it is wanted than thanin in any system In which wire circuits are dispensed dispense with wih The two actions I Imay may amy be roughly compared to the trans transmission transmission mission of sound waves from one point to another by b shouting in the open air all and by talking through a speaking tube A method metho of signaling through space which may m be b considered to t lie le between the te ordinary system with wih a wire wre circuit and ad the he modern wireless telegraphy is I that which which has ha been used us d to signal sigal i moving trains The car containing the receiving apparatus was fitted with a wire running the te length lengh of the roof or orthe orte orthe the te side and d the message was wa trans transmitted trans transmUted mUted from the pole line lne running alongside the track to the wire on the car by b induction through the space separating the two two This was the propagation of a true true ether wave ae dif differing fering ferng from front the te latest latet methods chiefly in the period and ad wave length of the the disturbance and ad in the sensitiveness and arrangement argement of the apparatus re responding responding to it i The development of the method metho now generally designated by the name n e wireless telegraphy will wl be described debe in the next paper I |