. Le journal technique du système Bell . un peu de temps après le coucher du soleil au terminal ouest et qu'ils commencent à diminuer avant de prendre le soleil au terminal est. En d'autres termes, les effets de la lumière du jour appearto s'étendent dans la période où le chemin de transmission le long de la surface des terres est non exposé aux rayons directs du soleil. L'effet de ceci est qu'avec l'avance de la saison de l'hiver à l'été, le moment où la valeur élevée de nuit-temps est pleinement atteint se produit et plus tard alors que le moment où il commence à tomber se produit plus tôt et plus tôt, jusqu'à la dernière partie d'avril quand ces derniers
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. The Bell System technical journal . some time after sunset atthe western terminal and that they begin to decrease before sunriseat the eastern terminal. In other words, the daylight effects appearto extend into the period in which the transmission path along theearths surface is unexposed to direct rays of the sun. The effectof this is that with the advance of the season from winter to summerthe time at which the high night-time value is fully attained occurslater and later whereas the time at which it begins to fall off occursearlier and earlier, until the latter part of April when these two timescoincide. .At this time, then, the transmission path no sooner comesinto the full night-time conditions than it again emerges. As theseason further advances into summer, the day conditions begin toset in while the night-time field strength is still rising. The proximityto the daylight hemisphere, which the transatlantic path reaches atnight during this season of the year is illustrated in Fig. 9. BELL SYSTEM TECIISICAL JOfRSAL. Fig. 10—Monthly averages of diurnal variation of signal field, Rocl< Ioim, I.. I. (2 X S) to New Southgate, England; 20.8 K.W. radiated power, 57, 000 cycles, 1923-1924 iH.is.iii..Lc RADIO ir.i.riiioM: ik.ixsmissiox a7 As the sunlit hcinispluTc ri-cfdos soutlnvard aftir the siimiiur solsticea tinu- is rtMclud. about the niiildli- of August, at vvhirh thf full uinlit-tiiui- valufs arc again ri-alizrd. liiyond this time they are sustainedfor increasing iHriiHJs of lime. It is of interest to note that at tiiesetwo limes of the year, ihe last of April and the middle of August, direct simlighl exists over the darkened hemis(ilure sonie aOO kiU)-melers above the great circle path. Kor all of ihe conditions noted above, n.inu-K, sunset, sunrise, .indsummer approach of the transmission path to the northern boundaryof the night hemisphere, the path lies in a region wherein the radiation