daily variation of the horizontal and dipping needles, &c. 341 
tion, changing its maximum from eleven o'clock in the 
morning to about four o’clock in the afternoon, yet the direc- 
tion of the motion was the reverse of what it was constantly 
found to be imdoors ; the cause therefore of this perplexing 
anomaly still remains to be discovered. 
It is proper to observe that Mr. Christie, having made 
some of his observations in-doors, and some in his garden, on 
two compasses at the same time, found the same reversion of 
motion in the two cases. His house is a mile distant from 
mine ; he has no stove in the room in which the in-door ex- 
periments were made ; and the only resemblance of situation 
is, that his window, like mine, is towards the north. It should 
be farther added, that this confirmation of the singular 
anomaly in question did not arise from his simply repeating 
my experiment, but grew naturally out of the particular 
mode he had adopted to prosecute the enquiry ; our experi- 
ments, with the exception of the first suggestion, are inde- 
pendent, and therefore, where they both lead to the same 
result, they may be considered as confirming the accuracy 
of each ; and where there is any difference, they will at least 
point out those circumstances which require farther investi- 
gation. 
P. S. The experiments to which I have alluded in page 337, 
made since this article was written, seem to indicate that this 
anomaly, as well as the circumstance there mentioned, may 
be occasioned by the daily varying intensity of the opposing 
magnets. 
