0 apparent decrease from the 56 - 58 zone to the 58 -60 zone is due to the lack of data in that region. The lower diagrams seem to indicate that the number of auroras seen in the northermost region (58 -60) varies relatively little throughout the year, but at lower latitudes during equinoctial periods the belt in which overhead auroras are seen becomes, on the average, broad. Such a study must be supplemented in the future, particularly in the regions to the north of gm lat. 58, by all-sky camera data. d) Sunspot cycle. It has long been suggested that the main belt of auroras contracts during...

This Encyclopedia aims, basically, at summanzmg the wealth of well established facts and outlining the relevant theories in the different branches of physics. With this as goal, the writers were asked to present their specific field in such a way that access is possible to any scientist without special a priori information in that field; the basic concepts of physics are assumed to be known to the reader. The survey given in each paper was also to be long lasting, so that even a few years after publication, each volume would be useful, for example as an introduction for newcomers or as a...

Sect. 14. 297 for such slow variations the effect described under 2. above will be by far the most predominant. In fact, the equipment provides a record of the time derivative of the element in question. 6) Records of the time derivatives of magnetic elements can, however, be obtained in a more direct way by recording directly the electromotive force (e. m. f. ) induced in suitably disposed coils by the variations of the geomagnetic field 10, 11. When a coil with the total winding area F is placed with its axis in the direction of a geomagnetic force component the variation of magnetic...

83 input to the ions is balanced by a cooling to atomic oxygen, the major neutral constituent, and measurements of the difference between ion and neutral tem perature permit the determination of atomic oxygen concentrations. Using this approach, ALCA YDE et al. 6 have shown from data taken above Saint Santin, France, that the atomic oxygen concentration at 200 km is slightly larger in winter than summer. () The molecular concentrations at heights near 200 km can also be derived from a determination of the ratio of the molecular-ion concentration to elec tron concentration, p (Cox and EVANS...

7 Fig. 3. Photographie de la lueur nocturne it I'horizon, obtenue it bord d'une fusee Aerobee it 184 km d'altitude Ie ler (l

45 downwards because (j on the average increases with height; but this conclusion does not follow from (18.3) when the dependency of Kc upon o is taken into consideration. s 2 ERTELl and PRIESTLEY and SWINBANK have shown that the upward eddy- flux of sensible heat must be larger than indicated by (18.3), because this formula does not account for the fact that rising eddies are systematically warmer than sinking eddies because of the effect of buoyancy. The reader is referred to the reviews by SUTTON 22], 23] and PRIESTLEY and SHEP- PARD 15) for further details concerning eddy-flux of heat...

Sect. 14. 297 for such slow variations the effect described under 2. above will be by far the most predominant. In fact, the equipment provides a record of the time derivative of the element in question. 6) Records of the time derivatives of magnetic elements can, however, be obtained in a more direct way by recording directly the electromotive force (e. m. f. ) induced in suitably disposed coils by the variations of the geomagnetic field 10, 11. When a coil with the total winding area F is placed with its axis in the direction of a geomagnetic force component the variation of magnetic...