14 
Proceedings of Royal Society of Edinburgh. [sess. 
tlie disturbance in both was from east to west. The focal distance 
of the latter instrument also appears to be slightly affected, due to 
motion of the mirror east and west ; it strengthens, therefore, the 
presumption that the direction of the waves must have had a strong 
easterly component. And the comparative feeble motion of both 
parallel to north and south direction, shows that the northerly 
component was present but was feeble. We shall now examine 
each trace separately. 
The photograph shown here (fig. 1) is a copy (enlarged about 2| 
Fig. 1. 
times) of the trace obtained from the declination magnetograph 
at the Colaba Observatory. The time of vibration of the magnet 
is 5 '33 seconds, and the original trace allows of an accuracy 
up to one minute in the determination of time. AB shows a 
part of the trace of the 12th June. The regular break seen on 
the trace is due to a metallic fan which automatically cuts off 
light every two hours for four minutes and a quarter. The middle of 
this break, therefore, represents 16 hours on the 12th June. The 
