February 1, 1900.] 



KNOWLEDGE. 



25 



V^IUUSTRATED MAGAZINE << 



Founded by RICHARD A. PROCTOR. 



LONDON: FEBRlAnY 1, 1900. 



CONTENTS. 



1! 



\V. Ill; TlN/.ELMANN, D.SC. 



Wireless Telegraphy 



(JUuslrated) 



The Evolution of Simple Societies. By Prof. Aifrbd 



C. HaIIPoS, M.A., P.SC. F.K.S. 



Polarity in IVlagic Squares.— I. liv E. I). Little. (Ilhs- 

 trattJ) 



The Fly •■ Syritta Pipiens. ' Bv Waltbb Wbscuk. {Illus. 

 frated) 



Photograph ot the Trifld Nebula V- IV. 41 Sagittaril, 

 and of the Region Surrounding. By Isjuc Robbhts, 

 D sc. F.B.s. (Plate) ... 



Astronomy and Astrology : A Question of Primo- 

 geniture. By K. Walteb Maunpbb, f.r.a.s 



Letters : 



Is THE iKIYBBSB INFINITE ? By W. H. S. MoNCK 



LrsAB Sbas. By a. Elvins 



S. S. Ctqni. By David Fiasebt 



Obituary ; 



.lOHK RrSKIN 



Dr. Elliott CorES 



Notices of Books 



Books Eecbited 



British Ornithological Notes. Conducted by Habbt F. 



WiTHBBBY, P.Z.S., M.B.O.0 ■ 



The Buried Alps. By Grenville A. J. Cole, m.b.i.a.. 



F.a.S. {Illustrated) ... 

 Long Waves of Winter Weather. By Alex. McDowall, 



M.A. (Illustrated) 

 Microscopy. By John H. Cooze, f.l.s., p.g.s. (Illustrated) 

 Notes on Comets and Meteors. By W. F. Dbnnino, 



P.B.A.B 



The Face of the Sky for February. By A. Fowleb, p.b.a.s. 

 Chess Column. By C. D. Locock, b.a. 



PAOK 



2.5 

 29 

 31 

 3.3 



3.5 



35 



38 

 38 

 39 



39 

 39 

 39 



W 



41 



41 



44 

 45 



4(i 



47 

 47 



WIRELESS TELEGRAPHY. 



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



In the ordinary commercial system of telegraphy, 

 signals are transmitted between two distant stations 

 by means of electric currents made to flow through a 

 circuit consisting of an insulated wire connecting the 

 two stations and the earth. The wire being connected 

 with *he earth, or " earthed," as the telegraphist 

 expresses it, at each of the stations in order to make 

 a complete circuio or loop round \ liich the electric flow 

 takes place. 



When a new system of sending electric signals in 

 which no connecting wire was required between the two 

 stations came into prominence it was named from the 

 most striking features to the ordinary observer, 

 namely the absence of the connecting wire. 



The name is not logically defensible, for on the one 

 hand the method of signalling known as " Wireless Tele- 

 graphy " involves the use of wires both in the trans- 

 mitting and in the receiving apparatus, and on the 

 other hand it includes systems of signalling which are 

 not popularly supposed to be electrical at all. 



The term aHlieric telegrapliy, which has also been 

 suggested, is just as open to the latter objection as the 

 one in common use, and personally I should be inclined 

 to suggest the term Hertz Wave Telegraphy or Hert- 

 zian Telegraphy, for the system of telegraphing without 

 connecting wi-es which is now exciting so much interest 

 and attention. Though greatly developed by the re- 

 searches of Lodge, Marconi, and others, Hertzian tele- 

 graphy depends entirely upon exciting at the transmit- 

 ting station and detecting i>t a distant receiving station 

 jether waves of a certain character, the existence of 

 wliich Iiad been deduced thcorelically by Professor Clerk 

 Maxwell, but first experimentally demons'^ratcd by the 

 late Dr. Hertz, of Carlsruhe, who ])ublished the results 

 in a series of papers in " Wiedemann's Annalen '' be- 

 ginning in July, 1887. 



It has long been an admitted fact that the observed 

 phenomena of light can only be explained by the exis- 

 tence of a highly elasic medium, to which the name of 

 huniniferous a'thcr has been given, and which must 

 fill at any rate the whole of the space into which our 

 vision can penetrate, that is to say the space intervening 

 between the earth and the most distant visible stars. 



The phenomena of light show, that for extremely 

 rapid motions such as light waves, which traverse some 

 186,000 miles in a second, this medium is far more rigid 

 than steel, while for comparatively slow motions such 

 as those of the planets (the earth's speed in its journey 

 round the sun is considerably under 20 miles a second), 

 it oflFers so little resistance that in most cases it is im- 

 perceptible to us. In the case of Encke's comet astro- 

 nomers believe they can just detect evidence of the 

 existence of a resisting medium in space, but that is 

 all. 



If any reader is disposed to object to the assumption 

 of a medium behaving in such very different ways with 

 regard to motions of different speeds, it may assist in 

 convincing him that the objection is not a valid one, 

 to direct his attention to the similar behaviour of such a 

 familiar substance as pitch. In moderately cold weather 

 this material has all the appearance of a solid, and will 

 resist a blow or momentary heavy pressure. If, how- 

 ever, a denser body than the pitch, such as a bullet for 

 example, be laid upon its surface, it will gradually sink 

 until it rests upon whatever is supporting the pitch. If 

 on the other hand the pitch is placed upon a less dense 

 body, such as cork, the latter will float up through it in 

 the course of time. The pitch, therefore, exposes great 

 resistance to rapid motion, but the smallest pressure 

 causes it to give way if sufficient time is given, or, in 

 other words, when the motion slows down sufficiently 

 the resistance becomes negligeable, thus offering very 

 close analogy to the behaviour of the luminiferous 

 sether. 



When a disturbance is set up in a medium, waves 

 are in general emitted in all directions from the point 

 of disturbance. Sound we know is transmitted by air, 

 and, unlike light, it will not traverse what we call 

 empty sjJace, viz.: — space occupied only by sether. 



Now, air and other gases are composed of molecules 

 in an irregular condition of agitation, which can be 

 shown to explain the observed fact that sound is trans- 

 mitted through air entirely by longitudinal vibrations, 

 that is to say, by waves in which the portions of the 

 vibrating medium move backwards and forwards in a 

 direction parallel to that in which the wave is travel- 

 ling. Vibrations in other directions are necessarily 

 started bv the disturbance which gives rise to 



