1911] RadioteJegraphy. 193 



WEEKLY EVENING MEETINCx, 



Friday, June L>, 1911. 



His Grace The Duke op Northumberland, K.G. P.O. 

 D.C.L. F.R.S., President, in the Chair. 



COMMENDATORE G. MaRCONI, LL.D. D.So. M.R.I. 



Radiotelegraphy. 



The practical application of electric waves to tlie purposes of wireless 

 teleo^raphic transmission over long distances has continued to extend 

 to a remarkable degree during the last few years, and many of the 

 difficulties, which at the outset appeared almost insurmountable, have 

 been gradually overcouie — chiefly through the improved knowledge 

 which we have obtained in regard to the subject generally and to tlie 

 principles involved. 



The experiments which I have been fortunate enough to be able 

 to carry out, on a much larger scale than can be done in ordinary 

 laboratories, have made possible the investigation of phenomena often 

 novel and certainly unexpected. 



Although we have — or believe we have — all the data necessary for 

 the satisfactory production and reception of electric waves, we are yet 

 far from possessing any very exact knowledge concerning tlie con- 

 ditions governing the transmission of these waves through space — 

 especially over w'hat may be termed long distances. Although it is 

 now perfectly easy to design, construct and operate stations capable of 

 satisfactory commercial w-orking over distances up to 2,500 miles, no 

 really clear explanation has yet been given of many absolutely authen- 

 ticated facts concerning these waves. Some of these hitherto ap- 

 parent anomalies I shall mention briefly in passing. 



Why is it, that when using short weaves the distances covered at 

 night are usually enormously greater than those traversed in the day 

 time, whilst when using much longer waves the range of transmission 

 by day and night is about equal and sometimes even greater by day ? 



What explanation has been given of the fact that the night dis- 

 tances obtainable in a north-southerly direction are so much greater 

 than those which can be effected in an east-westerly one ? 



Why is it that mountains and land generally should greatly ob- 

 struct the propagation of short waves when sunlight is present, and 

 not during the hours of darkness ? 



The general principles on which practical radiotelegraphy is based 

 are now so well known, that I need only refer to them in the briefest 

 possible manner. 



Wireless telegraphy, which was made possible by the fields of 

 Vol. XX. (No. 105) o 



