November 19, 19 14] 



NATURE 



21 



riie g^alvanised iron spiral behaved, however, just like 

 ii copper or brass spiral, because the oscillations did 

 not penetrate throujjh the thin layer or skin of zinc 

 into the iron. If, however, this zinc was oxidised or 

 broken, then the iron core exerted its effect in damping 

 the oscillations. 



Dr. Fleming then explained that when a radio- 

 telegraphic wave passes over the earth it penetrates to 

 >ome extent into it, and also loses amplitude owing 

 t > the absorption of wave energf\- by the soil. The 

 i'pth of penetration or depth in which the forces 

 itenuate to e' or to 0368 of their surface value, and 

 ne horizontal attenuation or distance in which the sur- 

 ace values decrease to the same fraction of their 

 original value can be calculated as shown by Dr. 

 Zenneck when the values of the soil conductivity, soil 

 lielectric constant, and frequency are known. Thus 

 iking the generally accepted values for sea water for 

 waves 1000 ft. in wave-length, the penetration into 

 rhe sea is at most about one metre. In the ordinary- 

 dry soil it may be 100 or several hundred metres. 

 There is a certain soil conductivity and wave-length 

 which gives the maximum attenuation of the wave 

 ver a given distance. 

 The calculation of the depth of penetration and 

 attenuation of the wave with distance can be made 

 when this soil conductivity and dielectric constant is 

 ciiown. Recent researches have show'n, however, that 

 he conductivity of imperfect insulators for alternating 

 currents is much greater than for direct currents. Dr. 

 Fleming referred to researches b)- himself and Mr. 

 Dyke for proof of this fact. Lately, he said, Mr. 

 Bairsto had continued this work in his labora- 

 tory for currents of extra high frequency of 

 one or more million, and found their dielectrics 

 had a maximum conductivit}' for a certain 

 high frequency. The inference from this was 

 that the earth was an incomparably better conductor 

 for the high frequency currents use J in radio-telegraphy 

 than for ordinary low frequency or steady currents. 

 Dr. Fleming then went on to consider the propaga- 

 tion of an electric wave over the earth's surface, and 

 pointed out that Sommerfeld had shown that when a 

 Hertzian oscillator had one half connected to the 

 earth there would not only be space waves through 

 the dielectrics (air and earth), but a surface wave 

 along the surface which would consist in longitudinal 

 electric currents propagated as a wave motion along 

 the surface. Dr. Fleming pointed out that this sur- 

 face wave might be the explanation of the well-known 

 facts that signals from long distance wireless tele- 

 -^-^raph stations can be picked up and detected without 

 ny high receiving wire, merely by connecting one end 

 I the receiver to the earth and the other to any in- 

 flated mass of metal in the interior, it may be, of a 

 .ouse. 



Passing then to the consideration of the diffraction 

 of long electric waves round the earth. Dr. Fleming 

 gave a brief account of the state of the theories 

 advanced by Poincare, Nicholson, Macdonald, and 

 Rybcz^nski. These agreed that the amplitude of an 

 electric wave sent out horizontally from any point on 

 the earth's surface diminished according to an 

 xponential function of the distance and wave-length. 

 ! he last-named analyst had shown that this function 

 was of the form /O-ooi*"-' \Jk where r is the distance of 

 the sending and receiving stations, and A is the wave 

 length. Actual observations by Austin over distances 

 up to 1000 miles had led to an empirical formula 

 differing only in that v'A appears instead of 

 v'X. 

 The bulk of the evidence so far collected as to long 

 NO. 2351, VOL. '94] 



distance transmission showed, however, that true 

 diffraction of space waves or even the surface waves 

 could not contribute more than a moderate fraction,^ 

 perhaps not 20 per cent., to the total observed result. 

 The chief part of the effect for distances of 3000 to 

 4000 miles must be contributed by space waves which 

 had reached the receiving station indirectly, that is, 

 after reflection or refraction at the surfaces of layers of 

 high-altitude ionised atmospheric gases in the manner 

 explained by Heaviside and by Eccles. 



The great variations in signal strength taking place 

 from day to day in long-distance wireless intercourse 

 proved that this must be the case. 



In conclusion. Dr. Fleming exhibited a chart show- 

 ing the variation in the strength of the signals re- 

 ceived at University College, London, from the Eiffel 

 Tower station in Paris at 11 a.m. each day during 

 last July, prior to the outbreak of war. The sudden 

 falling off on certain days was remarkable. Dr. 

 Fleming said that the further examination of the 

 cause of these variations was one of the chief objects 

 of the British Association Radio-telegraphic Committee 

 which was appointed at Dundee in consequence of a 

 suggestion made by him, and that as soon as the 

 present calamitous world-war came to an end it was 

 hoped these researches might be resumed. 



THE CAKADIAX ARCTIC EXPEDITION. 

 'X'HE Scottish Oceanographical Laboratorj-, which 

 -■- had much to do with the oceanographical 

 equipment of the Karluk, and especially the outfit of 

 the Scottish contingent, consisting of Mr. James 

 Murray, Dr. Alastair Forbes Mackay, and Mr. W. L. 

 McKinlay, is in receipt of a considerable amount of 

 official and private information concerning the Cana- 

 dian Arctic Expedition. The expedition was hurried 

 in its preparation and late in its departure, and the 

 plans were "still pretty fluid" on July 21, 1913. On 

 August 5 the Karluk was beset in 145° W., and 

 drifted west to Colville River by September 7, and 

 remained there until September 20, when she was blown 

 adrift by a gale. Stefansson and a party were ashore 

 hunting on September 19, and were thus stranded. The 

 Karluk drove north and west past Cape Barrow until 

 she reached 73"^ N., 162° E. ; then she drove south- 

 west and west until, on January 10 last, she was crushed 

 and sank in 38 fathoms sixty miles north bv east of 

 Herald Island. She drifted eight hundred miles at a 

 rate of seven miles an hour. A perilous escape was 

 made to Wrangell Island, at the heavy cost of eight 

 lives, to which were afterwards added three more 

 deaths on Wrangell Island, i.e. eleven in all. 



This death-roll includes all the scientific staff except 

 Mr. W. L. McKinlay, of Glasgow, a former assistant 

 to Dr. W. S. Bruce. The other scientific workers 

 missing or dead are Mr. James Murray, of Glasgow, 

 late biologist of the Scottish Loch Survev, naturalist 

 to the first Shackleton expedition, and worker upon 

 the Scotia invertebrates ; Dr. A. Forbes Mackav, of 

 Edinburgh, who had had wide experience in manv 

 spheres of active life, including the Royal Na\y, the 

 South African War, and was member of the partv 

 that first ascended Mount Erebus, as well as that 

 which reached the south magnetic pole under the 

 leadership of Prof. David; Mr. Beauchat, anthropo- 

 logist; Mr. Bjorn Mamen, topographer; and Mr. G. 

 Malloch, geologist. Besides these, Mate Anderson. 

 Second Mate Barker, and four seamen have also 

 perished. Captain Bartlett, of North Pole fame, with 

 an Eskimo, made an escape with difiicultv from 

 Wrangell Island to the mainland of Siberia, and 

 there, with the help of the Russian Governor, Baron 



