206 PECULIARITIES IN THE MAGNETISM 
about the year 1722,* the attention of philoso- 
phers has been directed to this curious subject ; 
and the observations and experiments of Canton, 
about the year 1758, f gave rise to the idea that 
the diurnal variations of the needle have a consi- 
derable dependance on the vicissitudes of the 
temperature of the globe, which, if exteriorly 
produced, must necessarily be associated with the 
solar calorific rays. 
3. Canton’s observations were corroborative of 
those of Graham, who found that the daily west- 
ward excursions of the needle commenced be- 
tween eight and nine in the morning, and arrived 
at a maximum about two in the afternoon, thence 
receding till next morning, when the needle re- 
commenced its westward advance. 
4, Canton’s extensive observations, which were 
carried on throughout every season of the year, 
enabled him to discover that these diurnal excur- 
sions of the needle were least of all in the winter 
season, and that they gradually increased through 
the spring months until the latter part of June, 
in correspondence with the advances of the sun 
from the southern to the northern tropic. ‘That 
* Phil. Trans. Abridged, vol. vii. 27. + Ibid. vol. xi. 421. 
