Page:The New International Encyclopædia 1st ed. v. 20.djvu/687

* WIRELESS TELEGRAPHY. 587 WIRELESS TELEGRAPHY. is charged Ui a liigli potiTitial ; it is cumiecteJ in series with tlic spark ;;a|i. 2, an<l the lunp ut wire, 3; when the jar is diseharged tliroiigh the gap electric osoiUations of liigli fre(|iieiicy are set up in the eirtuit; in virtue of the eireuit being closed — in contradistinction to the Ilcrtz open B FiQ. 12. lodge's syntonic jars. circuit oscillator — the oscillations are very per- sistent, that is, it requires a much longer time for their conversion into electric waves than in the o])en-cireuit type, but the emitted waves are much more feeble than where the oscillations are damped out rapidly. The receiving jar 1 15 is tonneeted through a sparlc-gap, 2, and a closed circuit, 3, 3, the induction of which is made variable by the sliding metal bar 4. When the feeble electric waves impinge upon the circuit they are transformed into electric oscillations, and by their cumulative effect the jar is charged to its sparking capacity when it breaks down the gap, thus indicating the presence of the waves. This action takes place if the jars, A, B, are in tune, i.e. if their inductance capacity and re- sistance are identical; but if B is not in tune or syntonized to A it will not respond. Syntonic or selective wireless telegraphy is based on these factors, but inasmuch as the open-circuit oscil- lations are damped out too quickly to obtain good resonance effects and the closed circuit oscil- lators are too feeble to cover long distances, these inherent difficulties have not been overcome with any degree of success in a practical way. Practical Considebations. In ordinary wire- less telegraph practice the first requisite is a powerful wave radiator and the second is a sensi- i'|:; s 5 •J ■1 4 4 1 ji 1 1 ! * i.l 1^ 9 ) 1 9- L0DGE-.l IHIIEAU 'rLiNED SVSTE.M. TllC first sj'stem of wireless telegraphy based on electric resonance was devised by Sir Oliver hodge of Kngland, and the oscillator and resonator are illustrated diagranimatically in Fig. l.'i. Kecent improvements, to be described, have been addeil to the original Lodge system both by Dr. Lodge and Dr. Alexander Muirhcad; the complete apparatus is shown in the accompanying plate. Referring to the diagram. A and B re|)rcsent the sending and receiving circuits respectively; 1, 2, and 1', 2', arc capaeit.y areas made of sheet metal in (he form of cnues; 1 and 2 are connected to the induction coil through the inductances. 5, H, and the condensers, 4, 4 ; these are provided for the purpose of increasing the capacitj' of the oscillator and for prolonging the oscillations in the circuit and to establi.sh a definite fre- quency of oscillation and the generation of long electric waves. The capacity areas 1' and 2'. li, are similar to those of A ; they are connected to the primary of >a transformer coil.O ; the secondary coil, 7, of the transformer is connected with the coherer, 8; the local battery circuits and indicating ajijiliances are not shown in the dia- gram, but are clearly shown on the accompanying plate. The coherer of which Fig. 14 is a diagrammatic view is of new type. It consists of a small steel disk a, rotating on a column of mercury, h, contained in the cup d: con- nection is made through the binding screw h and the platinum wire c: a copper brush, k. bearing on the shaft forms connection with the disk, a, thus completing the circuit. No relay is employed, but the coherer is connected direct to a siphon re- corder. The capacity areas and instruments are in- sulated from the earth by the supports 9. 9. A, B. In this system there are no earthed ter- minals; the object in eliminating the earth as a factor is that it represents a variable capacity, and by loading it on the oscillator and resonator tuning becomes exceedingly difficult. Slaby-Ahco Multiple Sy.stem. That the earth which seems so necessary to the successful transmission of electric waves over long dis- tances could be employed, Dr. Adolph Slaby and Fia. 14. LODGE COBKREU. Fig. 13. diagram of lodge tuned system. A, transmitter; B, receiver. tive wave detector. For this reason high aerial wires are employed, and both oscillator and reso- nator are of the open-circuit type. Excellent re- sults are assured without regard to the co- efficients of the circuits, for in this type of ap- paratus the periodicity of the oscillations and the length of the emitted wave may vary con- siderably without any untoward results. The apparatus shown in Fig. 6 was the first form of wireless telegraph employed by JIarcoui. and has been found to he the most practical to the present time. All the succeeding systems, whether syntonic or non-syntonic, are inodiflca- tions of this type. Vol. SX.^8. Fig. 16. diagram of slaby-akco system. Count Georg Arco of Germany devised the type of apparatus shown in diagram in Fig. 15, and by photogi'aph on the Plate (q.v. ). By math- ematical analysis it was determined that if the aerial wire was one-fourth the length of the