209 



20, 12.40, N.bvW. 2, 9.30, E.N.E. 

 2, 12.45, N. and S. (approx.) 2, 10.00, E.N.E. 



27, 2.00, N. by W. 22, 10.00, N.E. 



27, 2.30', N.bvW. 2, 11.00, N.N.E. 



2, 2.30, N. aiidS. 31, 11.00, N.N.E. 



26, 3.30, N.W. 20, 11.15, N. and S. 



p.m. 2, 12.00, N.N.E, 



4, 5.45, E. andW. 21, 12.00, N. by E. 



26, 5.50, N.W. (mean) 25, 12.00, N.N.E. 



September. 



21, l'.OO, N. and S. 5. 2.45, N.N.W. 

 1, 1.00, E. and W. (poor) p.m. 



4, 1.00', N. andS. 3, 11.00, N. bv E. (mean) 



4, 2.00, N. and S. 



At a glance, it is noted that the trend at midnight and 

 midday is usually N. and S., at 6 a.m. and 6 p.m. approx- 

 imately E. and W. Between these hours there is a regular 

 counter-clockwise swing. There is, therefore, a semi-diurnal 

 period. 



Considering the fundamental cause of this phenomenon, 

 the semi-diurnal character of the period is likely to be only 

 apparent, for such would be the case were the curtains always 

 directed towards the sun. 



After due consideration the following interpretation has 

 been adopted : That at Cape Royds, in the case of steady, 

 straight bands and curtains, they take up a position through- 

 out the day approximately directed towards the sun. The 

 period is therefore more truly diurnal. 



There are many cases where auroral forms, otherwise 

 similar to the generality of cases, seriously contravene the 

 above rule. These are regarded as exceptions. An examina- 

 tion of the tabulated statement of trends shows that they 

 agree with the rule stated to the following degree : — 



Coincident 60 ...... 51'7 % 



Approximately coincident ... 38 32*7 % 



Divergent ... 9 7*8 % 



Directly opposed ... ... 9 7*8 % 



8. Relation to Lines of Magnetic Force. 

 As it has already been shown that the average trend of 

 the arcs follows the sun round as the day progresses, there 

 can be no hard-and-fast relation to the magnetic meridia. 

 Much stress has been laid by observers in other parts of the 

 world upon a relation in this connection; but such is not 

 borne out by our observations at Cape Royds. There did, 

 however, appear to be a subsidiary influence on the control 

 ajid movement of arcs effected by the earth's magnetic field. 



