295 



In the course of these observations, the fluctuating state of the di- 

 rective energy was frequently rendered remarkably obvious, and in 

 one instance not only daily and hourly, but even momentary oscil- 

 lations were perceived. This observation induced Lieut. Foster to 

 examine the intensity of the magnetism during those oscillations, in 

 which a corresponding fluctuation was detected, and that so rapid, 

 as to compensate itself during the time of the needle performing 60 

 vibrations, though its effects were very sensible in intervals of only 

 ten. Accordingly, he was induced to refer this fluctuation in position 

 to a fluctuation in intensity as its cause. 



The next branch of this inquiry is directed to the dip of the needle 

 at the various stations visited by the Expedition, and especially at 

 Port Bowen ; when the mean dip was found, by a series of observa- 

 tions, extending from November 1 to June 27, to be 88 1' 23". 



The intensities came next under consideration. The relative in- 

 tensities at the different stations are first deduced by vibrating va- 

 rious dipping-needles in the plane of the magnetic meridian. This 

 gives the actual, or, as it may be termed, the natural intensity of the 

 earth's directive force, unreduced by the effect of the dip. But be- 

 sides this, Lieutenant Foster has instituted a separate series of ex- 

 periments at Port Bowen, in which the same needle, being alternately 

 suspended as a dipping and a horizontal needle, its times of vibration 

 under both circumstances were observed ; and from these observa- 

 tions the author thinks himself entitled to conclude that the changes 

 actually observed in the apparent intensity of the horizontal directive 

 force, are not due to any real and general change in the total mag- 

 netism of the earth, but arise only from a minute change in the dip 

 itself. He observes that, without entering into minute calculations 

 on the subject, he believes it will be found that if the magnetic pole 

 of the earth be supposed to describe a small circle about its mean 

 position, of about 2' or 2^' in radius, it will reconcile to a conside- 

 rable degree of precision nearly all the observations of the daily vari- 

 ations, both in direction and intensity of the horizontal magnetism, 

 both in Europe and in the arctic circle. 



These communications are terminated by an account of the repe- 

 tition of Mr. Christie's experiments on the magnetic properties com- 

 municated to iron plates by rotation, and with a paper of remarks 

 thereon by Mr. Christie himself. The observations are given in an 

 abstracted form, but accompanied with a statement of them in full 

 detail. In the course of these observations the phenomena observed 

 by Mr. Christie on a minute scale, were here, by reason of the ad- 

 vantageous geographical situation of Port Bowen, so strikingly deve- 

 loped as to excite the greatest interest in all who witnessed them. 

 A perfect correspondence was found between the direction of the de- 

 viation due to rotation, as observed and as predicted by Mr. Christie ; 

 and a numerical agreement in the results, as great as any expectation 

 could warrant, obtained. 



The whole of these results, Mr. Christie observes, prove that the 

 phenomena due to rotation arc not merely of theoretical but of prac- 

 tical importance, as connected with the problem of correcting the 



