780 Sir Oliver Lodge on the Transmission 



an observation of Mr. Marconi in a Royal Institution lecture 

 to the effect that the signals were weakest between Clifden 

 and Glace Bay when the boundary between day and night 

 was half-way across the Atlantic, tends to negative and 

 reverse this idea. 



If anything like a vertical reflector existed behind a 

 sending station (as just before sunrise, for instance) it might 

 lead to a temporary intensification of distant response. 

 Furthermore, any kind of opacity which increased with the 

 intensity of radiation, — and we shall proceed in a sequel to 

 consider such kinds, — would be more effective near a sending 

 than near a receiving station. The fact that sunrise or sunset 

 at either station — i.e. a horizontal beam — is specially effective, 

 whether as assistance or as obstruction, and the maxima and 

 minima which then occur, are very suggestive. For facts 

 of observation, see first the original discovery by Mr. Marconi 

 of the effect of sunshine, in the course of his fine experiment 

 of sending Hertz waves across the Atlantic and detecting 

 them at different distances and under different conditions 

 all the way across ; as described by him in Proc. Roy. 

 Soc. June 1902 ; also his Nobel Prize lecture, December 

 1909, quoted by Fleming, ' Wireless Telegraphy,' p. 82ti 

 (1910 edition). On the same subject Mr. Pickard made 

 observations in America, which are quoted by Professor 

 Pierce in his book on Wireless Telegraphy, page 135 ; Dr. 

 Austin, of the U.S. Naval Wireless Department, made 

 important measurements in 19 L0 which are quoted in Erskine 

 Murray's book, page 298 of the 1913 edition. In this book 

 indeed there is a general discussion of the whole subject, with 

 a summary of practical experience ; and there are doubtless 

 other data now available. Some recent ones by Messrs. 

 Round and Tremellen are recorded in the 4 Marconigraph , of 

 November 1912, where also a British Association discussion 

 at Dundee is reported. Special attention must be called to 

 the Addresses of Prof. Fleming and Dr. Eccles reported in 

 Nature, xc. p. 262, and in Electrician, 21 Sept. 1912; also 

 to Dr. Eccles' paper in Proc. Roy. Soc. June 1912. 



I see that Professor Zenneck in his important paper in 

 the Annalen der Physik, vol. xxiii. p. 862, makes a very low 

 estimate of the conductivity of ordinary air, and doubts if it 

 can effectively obstruct the passage of waves. But the fact 

 which he notes, that mist-laden air is more transparent to 

 long-distance signalling than clear air, speaks powerfully in 

 favour of the hostile influence of ionic conduction, or at 

 least of the adverse influence of free electric charges ; since 

 in mist the ions would have moisture condensed round them, 

 and would therefore be loaded so as to destroy the ready 



