SCIENTIFIC PROBLEMS IN RADIOTELEGRAPHY 369 



some irregular variations during the night. About an hour 

 before sunrise at Chelmsford, there was another sudden 

 decrease, followed by a rise and then a fall to normal day 

 strength soon after sunrise at Clifden. There is therefore one 

 maximum about sunset at Clifden and another at about sunrise 

 at Chelmsford. 



Mr. Marconi pointed out in a Royal Institution lecture at the 

 same date that in Transatlantic radiotelegraphy the signals are 

 at their weakest when the boundary between day and night has 

 moved into a position about half-way between the two stations 

 on opposite sides of the Atlantic. 



Other observers, such as G. W. Pickard, also have noticed 

 this curious dip or minimum in the signal strength curve at or 

 about sunrise and sunset. Similar variations are found to affect 

 the wave strength of the natural or stray waves. There are, 

 however, great variations in the phenomena due to wave 

 length and the position of the two stations in correspondence. 

 Hence we are very far yet from being able to lay down simple 

 general statements as to the facts or fit them to equally simple 

 explanations. 



Thus in the case of the Transatlantic transmission during 

 the day, conducted with waves 4,000 metres in length and 

 passing from Nova Scotia to Ireland, Marconi states that the 

 waves yield strong and steady signals during the day at Clifden 

 (Ireland) which gradually decrease in strength after sunset, 

 reaching a minimum about \\ hours afterwards; they then 

 increase again until sunset at Cape Breton (Nova Scotia) and 

 attain later on a high maximum value. During the night they 

 vary a good deal in strength. Shortly before sunrise at Clifden 

 the signals grow stronger and decrease to a lower value about 

 two hours later; they then return to normal day strength. 



Beyond a distance of 4,000 miles, signals have only been 

 received by night but Mr. Marconi has remarked that it is 

 curious that the signals sent out from Clifden should only 

 have been detectable in Buenos Ayres by night, whereas in 

 Nova Scotia they are no stronger at night than in the day. 

 He has also noted the curious fact that whereas ships 1,000 

 miles from England off the south of Spain or round the coast 

 of Italy can nearly always communicate with post office stations 

 on the British coast by night, yet the same ships when at an 

 equal distance away in the Atlantic or to westward cannot 



