368 SCIENCE PROGRESS 



addition to these horizontal radiations, rays are sent upwards 

 at various inclinations which impinge on the reflecting layer 

 and " illuminate " it, radiotelegraphically speaking, just as a 

 distant conflagration so far off as to be below the horizon 

 illuminates clouds in the sky or " lights up " the sky, to use 

 Dr. Eccles's expression. 



The suggestion is that, at very great distances, the waves 

 received, at least at night, are these reflected waves. In the day- 

 time, it is assumed that there is an additional ionisation, by ultra- 

 violet sunlight, of the air at still lower levels and that the effect 

 of this in accelerating the wave velocity of the upper part of 

 the wave front travelling through it is to bend down the rays 

 again earthwards, so as to make them fall short of the distant 

 receiving station. Perhaps also the interposition of the middle 

 layer of ionised air may reduce the perfection of the reflection 

 by the upper permanently ionised air. The two effects com- 

 bined are postulated as an explanation of the reducing action 

 of daylight on radiotelegraphy. Since the sunlit half and 

 the dark half of the atmosphere are in different conditions 

 as regards ionisation, at the boundary line there will be a more 

 or less confused state which might be likened to a liquid in a 

 state of froth : hence the propagation of a wave across the 

 boundary line is accompanied by difficulties or obstructions 

 which do not affect transmission in the more homogeneous 

 night half or day half of the atmosphere. 



Turning then to the facts of observation as regards the day 

 and night effects, some careful observations were made by 

 Messrs. Round and Tremellen at the Marconi Company's works 

 at Chelmsford last year, in July, which are recorded in a recent 

 issue (November 191 2) of The Marconigraph. They observed at 

 Chelmsford the strength of the signals sent out from the 

 Marconi station at Clifden in Ireland through a whole day and 

 night. Beginning say at midday, the strength of the signals 

 received at Chelmsford remained tolerably constant until about 

 an hour before sunset at Chelmsford. It then rose quickly to 

 about four times its day strength at a little after sunset at 

 Clifden. This rise was then followed by a sudden fall off in 

 strength again, which reached a minimum about an hour after 

 sunset at Clifden. About an hour later a very sudden increase 

 in strength set in which carried up the signal strength to nine 

 or ten times its minimum day value ; this continued with 



