996 PECULIARITIES IN THE MAGNETISM 
cessive application of the lamp: so that by fre- 
quently disturbing the poles by this process, the 
polar movements are much lessened. They are 
very conspicuous when the steel has been newly 
touched, but become much reduced by frequent ap- 
plications of the lamp, if not occasionally retouched. 
45. The lateral polar movements, by heat are, 
also, much lessened by frequent applications of the 
lamp; and in this respect, appear to be subject to 
the same law as the longitudinal movements; the 
greatest range being displayed on a newly touched 
magnet, and least of all by the last application of 
the lamp. 
46. From the above facts we are led to infer 
that, if the sun’s heat be the direct cause of diur- 
nal variation, the excursions of the needle will 
lessen by time, unless there be some sustaining 
force in operation ; and, therefore, are less now 
than formerly. This view of the subject presents 
one of the most important problems in terrestrial 
magnetism, especially when taken in connexion 
with the probability of the daily westerly excur- 
sions of the needle being greater than the space 
passed over by the eastward retrograde movements, 
and thus leaving a daily increment of westward 
