MaV 2, 1 901] 



NA TURH 



the received oscillations is increased, and the resistance 

 of the coherer more easily broken down. A somewhat 

 analogous arrangenient is used by Prof. Braun, to whose 

 work allusion has already been made in NATURE,' m 

 the transmitting circuit, the oscillations in the vertical 

 wire being set up by induction and not by directly 

 including the spark gap between the vertical wire and 

 earth. The results that have been obtained by Prof. 

 Braun are not, however, nearly so good as Mr. Marconi's 

 latest work. 



So far as tuning is concerned, Mr. Marconi appears 

 to have successfully got over this difficulty. Prof 

 Fleming, in the lecture above referred to, stated that the 

 communication between the Lizard and St. Catherine's 

 was multiple.^, it being possible to receive two or more 

 messages at once at each place. Mr. Marconi himself, 

 in an interview with an American contemporary, said 

 that with his improved apparatus he could send or receive 

 2, 10 or 50 messages at the same time, without any inter- 

 ference whatever. Particulars as to the method have 

 not, however, been published as yet, but it is to be hoped 

 that the details of the system will be e.xplained by Mr. 

 Marconi at his forthcoming lecture at the Society of Arts. 

 In Germany the subject of wireless telegraphy has 

 been tackled principally by Prof. Slaby and Count Arco, 

 who took up the subject in order to find a system for the 

 German Navy, to replace that of Mr. Marconi, the 

 Marconi Company charging, it was said, prices prohibi- 

 tive to any but the English Navy. Although the results, 

 so far as distance is concerned, which Prof. Slaby has 

 obtained are not very great, the system that he has 1 

 developed is one of great interest and seems to be \ 

 founded on sound scientific principles. Prof Slaby has 

 aimed throughout at getting rid of interference by pro- 

 ducing only oscillations of a definite wave-length and 

 tuning the receiver only to respond to these particular 

 waves. In order to produce the oscillations, the trans- 

 mitting circuit is arranged as shown in Fig. i. An 

 earthed loop of wire, ache, is used, instead of the single 

 insulated vertical wire usually employed, in one arm of 

 the loop there being a spark gap, ah, and a condenser, 

 K. The ends C and 11 of the vertical wires are joined 

 by a coil of wire as shown. In charging the condenser 

 the whole loop is used, but in discharging it is only the 

 arm AKC which is utilised, the coil of wire cn preventing 

 the oscillations passing into the remainder of the circuit. 

 Upon the length of the wire KC and the capacity of the 

 condenser K the wavelength of the oscillations depends, 

 and from their known values it can be calculated. 



Theoretical considerations showed Prof Slaby that the 

 free ends of both the transmitting and receiving wires, 

 i.e. the ends C and E (Fig. 2), are potential loops, and 

 that the earthed ends n and 1> are potential nodes. If, 

 now, to the receiving wire DE a second wire, DF, eqiial 

 in length to CD, is connected, there will be a potential 

 loop at F. At E and f, therefore, the potential will 

 vary over a much greater range than at u. If at f a 

 further length of wire, J, is attached, such that its length 

 is half a wave-length, then there will be established 

 between F and the free end, C, of the coil J a difference 

 of phase of 180°. At both points there will be potential 

 loops, but when the potential f has a maximum value in 

 one direction that at g will have a maximum value in the 

 oppos.te direction, and the potential difference between 

 F and G will be double that between f and earth. By 

 connecting the coherer between f and c; it can thus be 

 made to respond to received oscillations much feebler 

 than those which would be required to work it if it were 

 connected, as is usual, between u and earth. As an ad- 

 ditional advantage, the earth connection at D can be 

 removed, and the whole receiving apparatus thus ren- 

 dered earth free. 



Experiments have been made from time to time to 



1 Nature, igot, vol. Ixiii. pp. 403 .and 474. 

 KO. 1644, VOL. 64] 



devise a suitable repeater for use with wireless tele- 

 graphy, and the results of some work which has been 

 done by M. Guarini on this subject were recently pub- 

 lished in the Electrician} M. Guarini established 

 stations at Brussels, M alines and Antwerp ; messages 

 were successfully transmitted between Brussels and 

 Malines and also between Malines and Antwerp, and a 

 repeater was then set up at Malines with the object of 

 automatically transmitting the messages received from 

 Antwerp to Brussels. The experiments were not, how- 

 ever, very successful, as the repeater did not always 

 transmit the signals, and it was found, consequently, im- 

 possible to send any actual messages. A trustworthy 

 repeater for wireless telegraphy would be very useful, but 

 it is scarcely necessary to point out that it must be abso- 

 lutely trustworthy, as if a man has to be on the spot to 

 keep it up to its work he may as well be employed in 

 retransmitting the messages. 



In the meantime the wire-using telegraphists have 

 been by no means panic stricken by the achievements of 

 their wireless competitors, and some very notable deve- 

 lopments have taken place during the past few years. 

 We can only describe here a few of these ; those who 

 are more deeply interested in the subject may be 

 referred to Mr. Gavey's paper on telegraphs and tele- 

 phones at the Palis Exhibition, read recently before the 

 Institution of Electrical Engineers,'- in which will be 



K 



£i' 



iv5" 



found descriptions of all the more important improve- 

 ments effected in the last few years. One of the most 

 remarkable is the PoUak-Virag high-speed telegraphic 

 system. This system attracted considerable attention 

 both in the technical and lay Press when it was first 

 brought forward, towards the end of 1899, on account 

 of the extremely high speed of signalling which it was 

 said to be possible to attain by its use. It was reported 

 that in trials in America a speed of 60,000 words an hour 

 had been maintained over a line which was over 1000 

 miles in length, and that a speed as high as 100,000 

 words an hour had been attained. This is a very great 

 improvement on the 400 or 300 words a minute possible 

 with the Wheatstone automatic or Delaney multiplex 

 systems, which are those commonly in use in this country. 

 These remarkable results had been achieved by the use 

 of a telephone diaphragm as the receiving instrument, 

 the diaphragm being deflected by the currents received 

 through the telegraph line and a deflection in one direc- 

 tion corresponding to a dash and in the opposite direction 

 to a dot. The movements of the diaphragm were re- 

 corded photographically, a small mirror being attached 

 to the diaphragm and a ray of light being reflected 

 from this on to a revolving drum covered with a roll of 

 sensitised paper. The record had, of course, to be sub- 

 sequently developed in the ordinary manner. 



Since its first introduction the system has undergone 

 considerable development, a very ingenious modification 



1 The Electrician, March 22, 1901, vol. xlvi. p. Sig. 



= /o«r«iiifof the Institution of Electrical Eng ncers, 1901, vol. xxx. p. 73. 



