159 
nard observations, corresponds exactly with the epoch of 
minimum magnetic disturbance, as determined by General 
Sabine from the magnetical observations made at the colonial 
observatories and at Pekin ; and he shows that there is some 
probability that the period of the change in the rate of 
decrease also corresponds with the period of magnetic dis- 
turbance. 
In concluding, the Author tenders his grateful acknow- 
ledgements to Mr. Vernon, F.P.A.S., for the valuable assist- 
ance he has rendered him in procuring data, and in referring 
to original publications for the purpose of clearing up doubtful 
points; and he also remarks that without the means of 
reference afforded by the many valuable volumes of meteoro- 
logical observations now in the Society’s library, it would 
have been quite impossible to have undertaken an inquiry of 
this nature. 
