116 Commendatore G. Marconi [Marcli 13, 



A result of some scientific interest which I first noticed during 

 the tests on the s.s. Philadelphia was the very marked effect of sun- 

 light on the propagation of electric waves over great distances.* 



At the time of these tests I was of opinion that this effect might 

 have been due to the loss of energy at the transmitter by daytime, 

 caused by the dis-electrification of the highly charged transmitting 

 elevated conductor operated by the influence of sunlight. I am now 

 inclined to believe that the absorption of electric waves during day- 

 time is due to the ionisation of the gaseous molecules of the air 

 effected by ultraviolet light, and as the ultraviolet rays which emanate 

 from the sun are largely absorbed in the upper atmosphere of the 

 earth, it is probable that the portion of the earth's atmosphere which 

 is facing the sun will contain more ions or electrons than that portion 

 which is in darkness, and therefore, as Professor J. J. Thomson f has 

 shown, this illuminated and ionised air will absorb some of the energy 

 of the electric waves. 



The fact remains that clear sunlight and blue skies, though trans- 

 parent to light, act as a kind of fog to powerful Hertzian waves. 

 Hence the weather conditions prevailing in this country are usually 

 suitable for long-distance wireless telegraphy. 



Apparently the amplitude of the electrical oscillations and the 

 lengths of weaves radiated have much to do with the interesting 

 phenomena, small amplitudes and long waves being subject to the 

 effect of daylight to a less degree than large amplitudes and short 

 waves. I never considered that this daylight effect would be an 

 insuperable obstacle to transatlantic telegraphy, as sufficient sending 

 energy could be used during daytime to make up for the loss of 

 range of the transmissions. 



Turning again to Newfoundland, I ought to add that the experi- 

 ments could not there be continued or extended in consequence of 

 the hostile attitude of the Anglo-American Telegraph Company, 

 which claimed all rights for telegraphy, whether wireless or other- 

 wise, in Newfoundland. 



However, as I had received an offer of assistance from the Cana- 

 dian Government, it was decided to resume the tests between Great 

 Britain and Canada, and these tests were very greatly facilitated by 

 the subsidy of £16,000 granted by the Canadian Government to 

 support my experiments. 



The construction of another long distance station was, therefore, 

 commenced at Glace Bay in Nova Scotia, and very extensive tests 

 and experiments were carried on with Poldhu during the latter part 

 of 1902. 



* Proceedings Royal Society, Ixx. p. 344, ' A Note on the effect of Day- 

 light upon the Propagation of Electro-magnetic Impulses over long distances.' 

 Paper read June 12, 1902. 



t Phil, Mag., August 1902, Ser. 6, iv. p. 253, J. J. Thomson. 



