Deiembek 1, 1900.] 



KNOWLEDGE. 



281 



nothing, and in that instance for a wondor he was foiled, 

 for he never could persuade the world at large to believe 

 in his tot-al and absolute ignorance. In spite of the 

 hard names by which he was fain to describe his attitude 

 towards all theological dogma, we must remember that 

 be was continually sti-iving after light and truth. The 

 kernel of his religion was this, that men arc always 

 working out their own salvation — or the other thing ; 

 that we are all hour by hour receiving the rewiu-ds and 

 punishments of our own good and evil doings. 



But the book itself must be read. It will take many 

 behind the scenes of very unfamiliar playhouses, allowing 

 them to be present at the birth and obsequies of the / 

 Club, to take part in starting the Metaphysical Society, 

 to follow the thread of many a scientific adventure, and, 

 before thev have done, they will have realized, if they 

 did not know it already, that Huxley was not only a 

 peculiarly distinguished man of science, but also a 

 preacher of truth and righteousness, and not a preacher 

 onlv. 



WIRELESS TELEGRAPHY. V. 



By G. W. DE TUNZELMANN, B.SC. 



PRACTICAL WORK. 



With the exception of the unpublished experiments 

 of Professor Hughes leferred to in my last article, 

 nothing seems to have been done in the way of utilising 

 Hertzian electric waves for the purposes of telegraphic 

 communication before the year 1895. 



In April of that year, Professor A. Popoff, of the 

 Cronstadt Torpedo School, described to the Russian 

 Physical Society the apparatus shown in Fig. 1, which 

 he employed as a receiver for Hertzian waves. It con- 



Tei-tixxzl 

 JVire- 



-BcMcry 



Yin. 1. — Popoff's Hertzian Wave Keceiver. 



sisted of a tube coherer built in two sections, and having 

 one of its terminals connected with a vertical wire, and 

 the other with the earth. When a wave fell upon the 

 coherer, causing its resistance to fall from an almost 

 infinite value down to a few hundreds of ohms, a current 

 from the battery was enabled to flow through the circuit 

 and energise the electro-magnet of an ordinary Siemens 

 telegraph relay, thereby closing a circuit, not shown in 

 the illustration, containing a large battery and a tele- 



graphic recorder, which continued in action as long as 

 the current flowed through the battery in the coherer 

 circuit. As soon, however, iis coherence was set up, the 

 electro-magnet of the electric bell was energised simul- 

 taneously with that of the relay, and the bell-hammer 

 striking upon the central plate of the coherer caused 

 decohercnce, so that, unless the waves continued and re- 

 established the stat-c of cohesion, the recorder was thrown 

 out of action. 



Using a Hertz oscillator with 30 centimetre spheres, 

 Popoff was able to send signals over a distance of a 

 kilometre, which he extended to five kilometres, by 

 replacing the Hertz oscillator by a Bjcrknes one with 

 spheres 90 centimetres in diameter. 



Very shortly afterwards Captain Jackson made some 

 experiments for the Admiralty at Devonport, and suc- 

 ceeded in sending messages from one ship to another. 

 His apparatus, however, and the results obtained with 

 it, were treated as confidential and have not been 

 published. 



In June, 1896, Guglielmo Marconi, a young Italian, 

 and a pupil of Professor Righi, applied for provisional 

 protection for " Improvements in transmitting Electrical 

 Impulses and Signals and in Apparatus therefor," and 

 filed a complete specification on the 2nd of JVIarch, 1897. 

 At the time of making his provisional application 

 Marconi's apparatus was in a somewhat crude form, 

 but it contained important improvements in details, and 

 in July, 1896, he had the fortune of obtaining the assist- 

 ance and support of the Postal-Telegraph Department, 

 through the good offices of Sir W. H. Preece, who was 

 then the Chief Engineer of the Post Office. 



With this powerful co-operation, combined with his 

 own indefatigable industry and experimental skill, 

 Signor Marconi succeeded in overcoming a host of diffi- 

 culties, and in developing a comnfcrcially practical 

 system of telegraphy based on Hertzian electric waves. 

 ' The transmitting apparatus employed for long dis- 

 tances when it is not required to concentrate the waves 

 in a definite direction is shown in Fig. 2. 



Kio. 



-Lonir Di-tMiire \[ar(nrii TninsiiiiHei-. 



The small spheres, d, d, aie connected by the wires, 

 c', c', with the secondary termiii'.s.ls of an induction coil, 



c, and one of them is also connected with the vertical 

 wire, W, while the other is earth-connected. When the 

 Morse key, b, is depressed, the coil is energised by the 

 battery, a, and therefore, as long as it is kept down, a 

 stream of sparks is maintained between the spheres, 



d, d. 



When it is desired to send a btain of rays in some 



