PROCEEDINGS OF SECTION A. 57 



A comparison of the results obtained by the transmission of a 

 similar series of signals by the ordinary telegraphic arrangements and 

 recorded on the same chronograph showed a very satisfactory agreement, 

 the differences never exceeding 0*006 sees, or O'OOT sees., being thus 

 within the probable errors of observation. 



In 1909, MM. Claude Driencourt and Ferrie installed at the Wire- 

 less Station on the Eiffel Tower, at Paris, suitable apparatus for trans- 

 mitting and receiving time signals to and from stations at long distances. 



Clock signals coming from a distant station being too feeble for 

 automatic registration were received telephonically, together with 

 the beats of the local clock, and the comparison made by the method 

 of coincidences. By careful adjustments, the two series of beats could 

 be timed so as to make the detection of exact coincidence of beats more 

 certain and accurate. 



This is the principle which was found capable of application to 

 actual longitude measurements. 



In 1911, the Paris Observatory was connected with the Eiffel 

 Tower Wireless Station, and the determination of the difference of 

 longitude between that Observatory and Bizerte by the wireless method, 

 was undertaken.*. The distance between the two stations is over 

 920 miles ; the work was carried out with the greatest possible care 

 and the results were excellent. 



M. Baillaud, in his Annual Report on the Paris Observatory for 

 the year 191], page 19, makes the interesting statement that the time 

 required by the signals to cover the distance between Paris and Bizerte 

 was 0*p07s., showing that the velocity of propagation of Hertzian 

 waves is approximately the same as the velocity of light. f. 



Another important application of the wireless method was under- 

 taken in 1912 for determining the difference of longitude between the 

 Observatories of Paris and Uccle { (Brussels). 



On this occasion the clock comparison was made also in the usual 

 way by telegraph, and the efficiency of the wireless system may be 

 judged by the agreement of the results, which were as follow : — 

 Difference of longitude, Paris-Uccle — 



M. s. 

 By wireless ,. .. ■ .,8 4*965 



By ordinary telegraph . . . . 8 4*954 



* >I. Henri Renan. Detsrmination par la Telegraphic Sans Pil de la Difference de Longi- 

 tude entre Paris et Biz3rte, par MM. Lancelin et Tsatsopoulos, sous la direction de M. H. Renan. 



t Rapport Annuel sur I'Etat de rObservatoire de Paris pour I'Ann^e 1911. By M B. 

 Baillaud, Directeur de I'Observatoire. 



i Comptes Reudus. Vol. 156, N. 10, March, 1913, page 758. M. H. Renan. Resultats 

 de la discussion des Observations faites par MM. Delporte et Viennet, pour determiner par la 

 telegraphic sans fll la difference de longitude entre I'Observatoire royal de Belgique et 

 I'Observatoire de Paris. 



