diurnal Variation of the Magnetic Needle. 399 
be deduced, that would tend considerably to illustrate this 
curious and interesting subject, as yet involved in conjecture 
and uncertainty. I frequently, while at Bencoolen, observed 
that the needle did not retain the same level, but was some- 
times depressed, and sometimes elevated, six or eight minutes. 
I paid little attention to this, ascribing it to a minute alteration 
in the position of the point of the socket over the pivot. I ob- 
served, sometimes, a similar difference of level in the position 
of the needle at St. Helena, without being able to account for it. 
It may be possible, that the dip of the needle is subject to a 
diurnal variation in its vertical movement. I have perused such 
publications as have appeared on magnetism for some time 
past : they state no theory of this obscure science, more 
rational, or satisfactory, than that left us by the celebrated 
Halley. 
I have the honour to be, &c. 
JOHN MACDONALD. 
In the following observations, F. means fair ; A. after; 
R. rain; N. night; L. lightning; C. cloudy; S. sky; T. thun- 
der; m. much; o. overcast; s. serene; W. windy; 1 . little; 
a, the indefinite article ; E. or W. east or west variation : a 
figure, as 7, over the degree, means that the observation was 
taken then, and not at the usual hour.. 
