22 Lovering and Bond on Magnetic Observations at Cambridge. 
a conjecture in regard even to the variations of the shortest period 
from one year’s observations, however unremitted they may have 
been; but these observations may be of use in confirming a 
theory long entertained and well established by facts noticed in 
other places. 
The observations of Graham, in 1772, which resulted in the de- 
tection of the diurnal variation of the magnetic meridian at London, 
have been repeated since in various parts of the world with in- 
creased delicacy and skill and with the same general result which 
is briefly described. The magnetized bar, free to place itself in the 
magnetic meridian, does not remain in one fixed position during the 
day but sometime in the morning, between six and eight o’clock as 
the average statement, it starts in a westerly direction and moves 
that way till between one and three in the afternoon; then it be- 
gins to retrace its steps back to the east again. These points of 
maximum and minimum declination are formed in every diurnal 
curve and at nearly the same hour. We shall hereafter see what 
the limits of the time are. There are two ways in which the bar 
regains its first position. In some places, as Paris for example, it 
arrives at its greatest eastern elongation again between eight and 
eleven o’clock in the evening and then remains stationary till the 
time of morning excursion has come round once more. In other 
places, as at Cambridge, it travels eastward till evening and then 
goes back to form a secondary point of maximum westerly deviation 
about three o’clock, A. M.; after which it passes eastward and re- 
covers at eight o’clock the place it occupied 24 hours before. In 
certain cases, especially in northern latitudes, even when the sec- 
ondary maximum and minimum are not formed, the bar does not 
remain stationary during the night but occupies nearly all the time 
from three P. M. to eight A. M. in returning through the space it 
