June 29, 191 1] 



NATURE 



603 



can almost always communicate during the hours of dark- 

 ness with the Post Office stations situated on the coasts 

 of England and Ireland, whilst the same ships when at a 

 similar distance on the Atlantic to the westward of these 

 islands, and on the usual track between England and 

 America, can hardly ever communicate with these shore 

 stations unless by means of specially powerful instru- 

 ments. 



&CN«L DAYTIME OVER '^ 

 ^'^•^^''VHOLEflTLflNTIC Ku. 



StbotkI -^U 



StroncI 



ntopor 



STTOfK 



70()0 MLTRC5 



»«rm»'7tz:r/?r5 



• 5 NIGHT OVER Z z 



il-ui WHOLE fllLANTIC £q 



Z a OURINQ WHICH 4ICNRLS % _ 



n3 ^ »RE VERY v*m»BU O^Cj 



, . IN STRENCTH VARYINQ 



'Tl TROH -TlRirUtAK TO " 



VCRV STRONG . STORnSI 

 MXVt M OCCIOEO EF 

 ANO NOONLICHT HAV 

 AVE AN INrLUENCE 



Fig. 8. 



It is also to be noticed that in order to reach ships in 

 the Mediterranean the electric waves have to pass over a 

 large portion of Europe and, in many cases, over the 

 Alps. Such long stretches of land, especially when 

 including very high mountains, constitute, as is well 

 known, an insurmountable barrier to the propagation of 

 short waves during daytime. Although no such obstacles 

 lie between the English and Irish stations and ships in the 

 North Atlantic en route for North America, a night trans- 

 mission of 1000 miles is there of exceptionally rare occur- 

 rence. The same effects generally are noticeable when 

 ships are communicating with stations situated on the 

 Atlantic coast of America. 



Although high-power stations are now used for com- 

 municating across the Atlantic Ocean, and messages can 

 be sent by day as well as by night, there still exist periods 

 of fairly regular daily occurrence during which the strength 

 of the received signals is at a minimum. Thus in the 

 morning and the evening, when, in consequence of the 

 difference in longitude, daylight or darkness extends only 

 part of the way across the ocean, the received signals are 

 at their weakest. It would almost appear as if electric 

 waves in passing from dark space to illuminated space, 

 and vice versa, were reflected and refracted in such manner 

 as to be diverted from the normal path. 



Later results, however, seem to indicate that it is un- 

 likely that this difficulty would be experienced in telegraph- 

 ing over equal distances north and south on about the 

 same meridian, as, in this case, the passage from daylight 

 to darkness would occur more rapidly over the whole 

 distance between the two stations. 



I have here some diagrams which have been carefully 

 prepared by Mr. H. J. Round. These show the average 

 daily variation of the signals received at Clifden from 

 Glace Bay. 



The curves traced on diagram No. 8 show the usual 

 variation in the strength of these Transatlantic signals on 

 two wave-lengths, one of 7000 metres and the other of 

 5000 metres. 



The strength of the received waves remains, as a rule, 

 steady during daytime. 



Shortly after sunset at Clifden they become gradually 

 weaker, and about two hours later they are at their 

 weakest. They then begin to strengthen again, and reach 

 a very high maximum at about the time of sunset at 

 dace Bav. 



Thev then gradually return to about normal strength, 

 but through the night thev are very variable. Shortly 

 before sunrise at Clifden the signals commence to 

 strengthon steadily, and reach another high mnxiimmi 

 shorflv after sunrise at Clifden. The reccivi'd energy then 

 steadily decreases again until it reaches a very markr'd 

 minimum a short time before sunrise at dlace Bay. After 

 that the signals gradually come bark to normal day 

 strength. 



It can be noticed that, although th^ shorter wave gives 

 on the average weaker signals, its maximum and mini- 



NO. 2174, VOL. 86] 



mum variations of strength very sensibly exceed that of 

 the longer wave. 



Diagram 9 shows the variations at Clifden during 

 periods of twenty-four hours, commencing at 12 noon, 

 throughout the month of April, 191 1, the vertical dotted 

 lines representing sunset and sunrise at Glace Bav and 

 Clifden. 



Diagram 10 shows the curve for the first day of each 

 month for one year from May, 19 10, 

 ^ to April, 1911. 



" I carried out a series of tests over 



o longer distances than had ever been 



previously attempted in September and 

 October of last year between the 

 stations at Clifden and Glace Bay, and 

 a receiving station placed on the Italian 

 Bs. Principessa Mafalda, in the course 

 of a voyage from Italy to the Argentine 

 (Fig. II). 

 (iRtCNwiCMTiMt During these tests the receiving wire 

 was supported by means of a kite, as 

 was done in my early Transatlantic 

 jtests of 1901, the height of the kite 

 varying from about 1000 to 3000 feet. Signals and 

 messages were obtained without difficulty by day as well 

 as by night up to a distance of 4000 statute miles from 

 Clifden. 



Beyond that distance reception could only be carried out 

 during night time. At Buenos Aires, more than 6000 

 miles from Clifden, the night signals from both Clifden 



VAlllATIUM.OiMAtS 



. IMFIMA 

 nillllllC AraiL l!>ll 



,j — kA 'r\j- 



'j yv 



ij kA j--^ 



t i !v^ 6cr 



AJft.RIATION OF SIGNALS 

 AT CLIFDEN 



FROM MAY 19J0 to APRIL 1911 

 CURVE FOR FIRST DAY OF 

 EACH MONTH BEING SHEWN 



'•^^' '- urn , \"H"i^^:^T. . ...l^agf .V?'i 



ai kA 



■♦I v\ 





=!=>^*4^ 



±uU:^ 



»t=riA*si(=p 



OECl 





Fig. 9. 



Fig. 10. 



strength 



and Glace_ H.i\ w^r.' generally gcxnl, luii 1 

 suffered some variations. 



It is rather remarkable that the radiations from Clilden 

 should have been detected at Buenos Aires so clearly at 

 night time and not at all during the day, whilst in Canada 

 the signals coming from Clifden (2400 miles distant) are 

 no stronger during the night than they are by day. 



Further tests have been carried out recently for the 



