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| XV.— Results of the Makerstoun Observations, No. II. On the Relation of the Varia- 
tions of the Vertical Component of the Harth’s Magnetic Intensity to the Solar and 
Lunar Periods. With a Plate. By J. Attan Broun, Esq., Director of General 
Sir T. M. Brispanr’s Magnetical and Meteorological Observatory. Communi- 
cated by General Sir T. M. BrisBane, Bart. 
(Read 20th April 1846.) 
1. The following results are deduced from the observations of the balance or 
| vertical force magnetometer, which consists of a magnetic needle, balanced hori- 
zontally, and resting, by a knife-edged axle, on agate planes. Much doubt has been 
| entertained as to this instrument’s capability of shewing changes of moderate 
| nicety, and it has been considered altogether unavailable for changes of long 
| period :* it has been shewn (Vol. XVI, p. 67), that there are several difficulties 
| in the way of an accurate interpretation of the observations, independent of the 
| instrumental capacity. If it be added, that disturbances seem to affect the daily 
| means of the vertical component,} in a more serious way than they do those of the 
horizontal component, it will be seen that there are a series of difficulties, which 
tend to render good and consistent results from the balance magnetometer nearly 
_unattainable. It will be judged afterwards how far these difficulties have been 
| overcome in the present instance. 
2. The changes of the vertical component are, in general, very gradual and 
| regular; even during considerable disturbances the balance needle moves gradu- 
| ally to an extreme position, remaining there, with moderate fluctuations, for a 
_ considerable period, and afterwards returning slowly to its mean (or nearly mean) 
| position; the bifilar magnet, on the contrary, moves with considerable rapidity 
from one extreme position to another. This difference in the mode of distur- 
bance, I do not conceive due to a want of sensibility in the balance needle, but 
rather to a difference in the nature of the disturbances of the dip, and of the total 
intensity. | 
3. The changes of the vertical component, then, during disturbances, will 
evidently have little or no effect on the regularity of the diurnal curves, although 
the periods of maxima and minima may be affected; it will be different for the 
daily means, for, as the disturbances will, in general, be almost wholly negative 
* Revised instructions by a Committee of the Royal Society of London, p. 37. 
+ I shall generally use the terms vertical or horizontal component, instead of vertical or horizontal 
force ; the latter are not at all expressive where the changes may be altogether due to variations of dip. 
VOL. XVI., PART II. 2M 
