January 12, 1899] 



NA TURE 



251 



is little to choose on the merit of distance. On the other 

 hand the speed of signalling by the " Marconi '' system 

 is limited to something like twelve words a minute, and 

 we must conclude that it is this circumstance that 

 handicaps the method. It is also probable that "coherer" 

 systems are at present too susceptible to mechanical and 

 fortuitous electrical tremors for the ordeal of a telegraph 

 office, but in the absence of evidence it is perhaps scarcely 

 fair to draw comparisons in this regard. According to 

 the Times of Monday, the 9th inst., arrangements are 

 being made under the direction of Signor Marconi at the 

 South Foreland lighthouse, and aboard the South Good- 

 win light-ship, for a series of e.xperiments with his 

 apparatus. It is stated that if the system is found satis- 

 factory it will forthwith be adopted between those points 

 — the distance between them is about three miles. 



Two articles in the Elrctriiian of November 12, 1897, 

 one by Dr. Lodge' and the other by Mr. A. C. Brown, 

 should be referred to as indicating the e.xtent of the 

 work done and the hopefulness of the votaries of 

 "coherer" systems at that time. Later developments of 

 the "coherer" system, particularly in the matter of 

 syntony and the best arrangement of contacts, are dealt 

 with by Dr. Lodge in a communication to the Physical 

 Society of January 21, 1898, an account of which appeared 

 m N.VTURE in February 1898. The possibility of in- 

 dividualising signals by syntony on Dr. Lodge's system 

 is discussed in an e.xcellent article in the Electrical 

 Review of August ig, 1898, which is prefaced by some 

 remarks that already show the weak points of "coherer" 

 systems. Messages had then been sent by Marconi over 

 a distance of about si.xteen miles, and received in "dot 

 and dash " on the Morse ribbon at a rate of something 

 under twelve words a minute ; but it had been found in 

 practice that the principle of resonance could not be 

 applied with sufficient effect to ensure that messages 

 should be recorded only by a single selected receiver. 

 Whether the later more elaborate methods of syntony 

 for "coherer" systems, proposed by Dr. Lodge, have 

 justified themselves in practice is not yet known, but it 

 is a significant fact that Dr. Lodge's most recent paper 

 on the subject of space-telegraphy makes a distinct 

 departure from the "coherer" system, and contains no 

 account of experiments in the direction of syntonised 

 receivers used in this particular way. 



In 1898, e,xperiments as to the mysterious connection 

 between " coherers " and photO;electric phenomena made 

 little progress towards a practical system of telegraphy. 

 In the hands of Prof. Minchin these e.xperiments, at the 

 outset, showed great promise ; they gave us the " collect- 

 ing wire" which, protruding into space, acts as a "feeler" 

 for Hertz waves, but at present they remain as toys of 

 the laboratory. The so-called " Lichtelektrische Tele- 

 graphie " of Prof Zickler, of which a very good account 

 is given in the Elelitrolcclinische Riiniishau, No. 21, 

 pp. 233-233, i8g8, is more pretentious as a means of 

 signalling. Prof. Zickler makes use of an old discovery, 

 due to Hertz, that ultra-violet light is able to reduce the 

 spark-resisting power of an air-gap. He directs a beam 

 of light from an arc lamp, provided with a shutter, upon 

 the extended spark-gap of an induction coil, and by 

 opening and closing the shutter causes sparks to pass at 

 the gap at corresponding intervals of time. These 

 sparks affect a "coherer" circuit, and signalling is 

 rendered possible. Such experiments are very attractive 

 from a purely scientific standpoint, but it is not easy to 

 see the advantage of this method as compared to the 

 ordinary heliograph. Using the simplest form of appa- 

 ratus. Prof Zickler succeeded in signalling by this means 

 across a space of two metres ; and by the aid of an arc 

 lamp that expended nearly two horse-power, and by the 



1 By a slight error, Dr. Lodge there attributes an experiment on liquid 

 "coherers" to Lord Rayleigh. This experiment was lirst described and 

 shown by the present writer on March 26, 1897, at the Physical Society. A 

 few weeics later it was repeated by Lord Rayleigh at the Royal Institution. 



use of quartz lenses, that distance was extended to 200- 

 metres. The speed of receiving the signals is not 

 mentioned ; the e.xtreme limit is probably about twelve 

 words a minute. He proposes to apply the system to 

 lighthouses and to fortresses. We admit that such a 

 system would be admirably suited for the purpose of 

 warning ovtx foes off dangerous parts of the British coasts ; 

 but for the purpose of warning our own or friendly 

 ships, a surer means of communication must be adopted. 



Comparing the various methods,' and keeping in mind 

 that we are here concerned with a practical question for 

 engineers, rather than with the scientific aspect of space- 

 telegraphy, it would seem that the " coherer " systems as 

 a whole are about to be cast aside, and that preference 

 is to be given to alternate-current inductor systems for 

 coast-telegraphs. If this is indeed to be the case, the 

 problem is greatly simplified, and experiment resolves 

 itself into the single task of finding the best design of 

 apparatus for communicating between a moored light- 

 ship and the shore by means of inductor coils. Dr. 

 Lodge's paper on "Improvements in Magnetic Space 

 Telegraphy" gives us what may be regarded as the 

 academical aspect of that task ; he describes a new 

 receiving device for magnetic induction telegraphy, and 

 he explains the method of putting it into practice. The 

 principal feature of this device is the outcome of an 

 electric resonance experiment first described in N.\ture, 

 vol. -nH. p. 368, eight years ago — namely, the experiment 

 of syntonic Leyden jars. Dr. Lodge now replaces the 

 jars by condensers, and the "tuned circuits" take the 

 form of horizontal coils of wire. The inducing coil is 

 connected to an alternate-current dynamo, and the 

 induced coil is connected to a train of telephone relays, 

 the last of which is thus set into violent action at each 

 received impulse. The paper includes the theory of 

 two such circuits arranged in mutual syntony, and it is 

 full of information and suggestions as to the proper 

 course future experiment should take ; the advantage of 

 syntony is discussed, and the relative importance of 

 conduction and induction is considered together with a 

 detailed investigation of the theory of " detectors " for 

 such a system. 



The absorption-factor in the case of sea-water will 

 probably be one of the first matters to be dealt with by 

 experiment and theory in the present year. By the use 

 of horizontal inductor coils, one on the light-shjp and 

 one ashore. Dr. Lodge avoids the practical difficulty ; 

 nevertheless the problem is sure to elicit his interest. 

 Mr. Whitehead, holding tacitly to Maxwell's equations, 

 deduces a law for the absorption-factor, and to this law 

 Dr. Lodge takes exception. Maxwell supposed that the 

 total current was made up of the polarisation current 

 and the induction current ; Mr. Whitehead assuines that 

 the polarisation current may be neglected, and that 

 provided the frequency is not comparable with that of 

 light, no serious error can arise from that assumption. 

 Do Maxwell's equations fail then for such a case ? Dr. 

 Lodge seemed unwilling to admit that they do fail ; he 

 suggested that Mr. Whitehead had written them down, 

 in a form that did not agree with Maxwell, and that 

 Prof. J. J. Thomson had written them in yet another 

 form. Mr. Whitehead now asks Dr. Lodge what is the 

 right form ? And that's how the matter stands. 



ROLLO APPI-EVARD. 



THE FISHES OF TANGANYIKA AND 

 OTHER GREAT LAKES. 



THE first part of the fifteenth volume of the Trans- 

 actions of the Zoological Society of London, which 

 has just been issued, is devoted to a report by Mr. G. A. 

 Boulenger, F.R.S., on the collection of fishes made by 



1 For the various methods of space-telegraphy, see a paper by Dr. S. P. 

 Thompson (Soc. Arti Journal, 46, pp. 453-460, 1898;. 



NO. J 524, VOL. 59] 



