in the position of the horizontal needle , &c. 
*73 
In the foregoing observations, when the north end of the 
needle was directed towards the east or west points of the 
compass, it will be seen, that the various deflections of the 
needle rendered it difficult to discover which way its north 
end had proceeded during the time of westerly daily variation. 
This anomalous action of the needle exhibited itself so 
strongly on the 23d of February, that I was induced to com- 
pare the nature of some of its deflections, with simultaneous 
observations, on the times of vibration of a freely suspended 
horizontal needle ; and as I found, in every instance of com- 
parison, a decided relation between the changes of horizontal 
intensity, and these deflections, I began to watch the action 
of this needle more closely, at the times that fluctuations in 
the directive force of the horizontal needle, had hitherto been 
observed to take place ; and from its indications, I frequently 
stated to the Gentlemen making the observations on hori- 
zontal intensity, what I considered would be the nature of the 
intervals they were about to obtain ; which proving correct, 
no longer left any doubt on my mind, of the cause of thesa 
apparent irregularities. In order, however, to point out 
more satisfactorily the relation between the changes of 
horizontal intensity, and the various deflections of this 
needle, at other positions of its north end, I have annexed the 
observations on the times of performing 60 vibrations by a 
horizontal needle, taken during the same time ; but this will 
not explain all the anomalies alluded to, without also stating, 
that the fluctuations which frequently took place in the 
intervals of 10 vibrations, were sometimes observed to com- 
pensate one another, so as, in the mean of sixty, to leave no 
