342 



Results of Makerstoun Obsebvations, 1844. 



TABLE XI. — Variations of Magnetic Declination with reference to the Moon's Hour-Angle for each 

 Lunation, for the Six Summer and Six Winter Lunations, and for the whole Twelve Lunations 

 of 1844. 



Table XL has been formed from the hourly observations between January 6 and December 24, 1844, 

 including 12 complete synodical revolutions of the moon. In each lunation, the hourly observations nearest 

 the moon's transit of the meridian, were summed as 0, the next following as 1, and so on up to 23 or 24; 

 when only 24 observations occurred between two successive transits, the observation nearest the second of the 

 two transits was summed both as 24 and 0. The numbers in the first column are, therefore, |fths of the 

 moon's hour angle from the meridian. 



Diurnal Variation luith reference to the Moon's Hour-Angle. — The separate lunations present considerable 

 irregularities, as might be expected where the range of the variations is so small ; an inspection, h(jwever, of 

 the separate residts, renders it extremely probable that the law of variation is somewhat different for the 

 lunations in which the moon is in opposition north of the equator, and for those in which it is in opposition 

 south of the equator. The variations have accordingly been determined for these two groups, namely, for the 

 1st, 2d, 3d, 10th, 11th, and 12th lunations, and for the remaining 6 summer lunations. In order to 

 destroy the minor iiTegularities, the following means of variations are deduced, the mean for the moon on the 

 meridian (O*") being the mean of the three values for 24, 0, and 1, in the previous Table, and each of the 

 other values being the mean of two : — 



When the moon, therefore, is in opposition north of the equator, the diurnal variation of the magnetic 

 declination due to its varying hour-angle consists of a maximum of westerly declination when the moon's 



