Qa 
[PRELIMINARY REPORT ON TERRESTRIAL MAGNETISM. 19 
time spent in observations than any force magnetograph. Also no tempera- 
ture correction is required, and there is no variability in the scale value. 
The expediency of introducing changes which are unlikely to be generally 
adopted is not a question on which general agreement is at all likely, but it 
is perhaps as well the question should be ventilated. 
A similar remark applies to a second practice introduced at Potsdam, 
viz., taking mean values, not for 60 minutes centring at an hour, but for 60 
minutes commencing at an hour. There are arguments of some weight for 
the change, and they would be weightier than they are if there were no such 
things as drift in instruments or natural n.c. changes, which stand in the 
way of treating the day as an isolated unit. This is a case in which 
magneticians might exchange ideas with meteorologists, as the problem 
presents itself in meteorology in a variety of connections. 
$7. There are two matters, less obviously of international interest, 
which call for notice, even in a preliminary report, viz., the relation of 
magnetic disturbance to Aurora, and the taking of observations in high 
latitudes. The discovery by Professor Stormer, of Christiania, of a prac- 
tical method of securing photographs of Aurora and reference stars, and 
of thus determining auroral heights and positions, has rendered possible a 
comparison of auroral and magnetic phenomena likely to throw fresh light 
on magnetic disturbances, and to provide a means of developing and 
checking theory. If this country is to participate in this promising field of 
discovery, provision must be made for auroral observations. 
Eskdalemuir is, of course, much better situated for such a purpose than 
any observatory in the South of England or Ireland, but not nearly so well 
situated as an observatory in the extreme North of Scotland. Some parts 
of Canada would probably be even more suitable for this purpose. 
The other subject is the desirability of securing continuous magnetic 
records in very high latitudes. The records obtained by Professor Birke- 
land in the Arctic, and those obtained by recent Antarctic expeditions, 
show conclusively that these are the regions where really momentous things 
in terrestrial magnetism have a way of happening. Records from high 
latitudes may prove a key to many magnetic problems. 
