As in the ease of the Cape Evans observations, mean character numbers 

 corresponding to various lypcs of aurora have been compiled and are shown below : 



Coloured aurorse, Cape Adarc . . Mean magnetic character number, 1 20. 

 "Clear, no aurora." .. ,, ,, ,, ,, 0-75. 



From the above figures, it seems fairly clear that periods of brilliant and coloured 

 anrorao are definitely related, on tJte average, to magnetic disturbances at the same 

 ! ion, and that the same relation can also be definitely traced between aurorse and 

 magnetic disturbances as far apart as Cape Evans and Cape Adare. 



As magnetic disturbances (when their occurrence can be traced at a number of 

 magnetic stations) appear to occur simultaneously, or almost simultaneously, over 

 the earth, we might expect to find that increased brilliancy of auroral display would 

 also occur simultaneously. This increased brilliancy might, however, only be 

 observable at certain favoured places, especially if increased brilliancy were associated 

 with some displacement of the paths of the individual spirals as they approached the 

 earth. We might, therefore, expect a closer correspondence between auroral intensity 

 and magnetic character number if simultaneous auroral data were available from a 

 number of widely separated stations, particularly if due account was taken of the 

 normal intensity of aurora at the hour in question. Though we cannot state definitely 

 that a brilliant auroral display may not occur somewhere for every magnetic 

 disturbance, there seems to be no doubt that every striking auroral display in high 

 latitudes is not associated with a simultaneous magnetic disturbance. The correlation 

 between aurorse and magnetic disturbance cannot therefore be complete, suggesting 

 that the magnetic disturbances may not be due to the same particles, which give rise 

 to the aurora ; they might, however, be due to similar particles which do not converge 

 towards the magnetic axis of the earth. 



Mention has previously been made of the fact that auroral displays show a 

 tendency to continue for long periods, and the same is true, in some degree, of magnetic 

 disturbances. It is, therefore, very necessary to examine the magnetic conditions 

 preceding and following the hour of maximum auroral display, to determine if the 

 correspondence is a real one, and to make certain that the maximum of the mean 

 character number is simultaneous with the greatest intensity of aurora. This analysis 

 is all the more necessary if we recollect that the production of alpha rays l>y 

 radio-active disintegration in the sun must be accompanied by the production of 

 beta and gamma rays. All of these rays travel with different velocities and therefore 

 should reach the earth's atmosphere after different intervals of time. 



The necessary reductions have been made completely for 1911 in Classes I, II, 

 III and IV of aurorse seen at Cape Evans, and in Classes I and II of aurorse seen at 

 Cape Adare. These figures are given below in Table 10 and shown in diagrammatic 

 form in fig. 4. In this Table, ( 1) and (n- 1) represent, respectively, one hour 

 before and one hour nHrr ih,> IJ M ,P corresponding to the occurrence of aurora? of the 

 class mentioned. 



36 



