In the first instance, the Table shows that the diurnal variation of frequency for 

 faint aurora? is of the normal type, with a principal maximum at 4 hours. The 

 numbers of aurora? of average brightness and over are, on the contrary, much more 

 evenly distributed throughout the day, and it will be observed that there is a strong 

 family resemblance to aurora? showing colour and movement, particularly as regards 

 the afternoon maxima and minimum. 



(It will be noted that the combined figures for faint and bright auroras give a diurnal 

 frequency with maxima at 4 hours and 18 hours, and a minimum at 19 or 20 hours ; 

 these times being little different from those derived from figures relating only to the 

 darkest days of the year.) 



As is to be expected, the value of the ratio number of observations of no aurora 

 (when conditions were favourable for observations) to the number of occasions when 

 aurora was observed varies during the course of the day, the smallest value of this 

 ratio being in the morning (1-0) and the largest value in the evening (2-3). 



It is unfortunate that the number of observations is so small, but at least it is 

 clear that the number of bright aurora? exceeds the number of faint aurora? in the 

 afternoon, while the reverse is true in the forenoon. 



The figures for the few aurora? classed as " very bright " and " bright " give an 

 even more definite result, the number of such aurora? seen in the afternoon being 

 actually greater than the number in the forenoon, while for the " very faint " class 

 the morning observations of aurora? are three times as numerous as the afternoon 

 observations. 



The hours when aurora? are most likely to be brilliant are, therefore, the hours 

 when aurora? are least likely to be seen at high altitudes from Cape Evans that is, 

 close to the station. Faint aurora?, on the other hand, are most likely to occur at 

 times when aurora? are most likely to be seen close overhead. 



Diurnal Frequency of " No Aurora." 



In Table 8 is also shown the number of occasions at exact hours when the weather 

 was clear and suitable for observation of aurora?, though none was seen. The period 

 in question was the whole period from April 24th to September 30th, 1911. 



As might no doubt be expected the minimum occurs at 4 or 5 hours, but the 

 maximum occurs at 22 hours, two or three hours later than the general aurora minimum. 

 Neither maximum nor minimum is, however, sharply defined, and this is possibly to 

 be expected when it is considered that the number of negative greatly exceeds the 

 number of positive observations. 



17 



