‘ 
XiV GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
also be stated as very probable, that the errors in the corrections employed (to reduce the means obtained to 
those derivable from complete series) are insufficient to account for the differences of these variations from those 
for the preceding years ; as is evident for the year 1847, corrected by two very different methods. The only 
evident explanation remaining is to be found in the varying secular change for these years; and it does not 
appear at all improbable that the difference is connected with this variation. It has been shewn that the annual 
period has appeared inverted when the sign of the secular motion was opposite ; it is the most remarkable fact 
in connection with the differences of the results for the two periods 1843-6 and 1847-9 that they are exactly 
the inverse of each other (see columns 8 and 13 of Table 3): the completeness of the opposition in the double 
maxima and minima appears too curious to be accidental. _ If the latter result be a true exposition of the annual 
law for these 3 years, it will follow that the inversal of the law observed at the same time with an opposite 
secular motion is not necessarily a consequence of that opposition.* 
Differences of the Daily Means of Declination from the Means for the corresponding Months.—The discus- 
sion for 1844 will be found in the volume for that year, page 332, the results for 1845 and 1846 are obtained 
from Tables I. and LI. of this volume. 
TABLE 4.—Means of the Westerly and Easterly Departures of the Daily Mean Magnetic Declination 
from the Monthly Means, with their Differences. 
Mean Westerly Departures. | Mean Easterly Departures. Mean spine eS referen cesta 
Month. 
1844, | 1845. | 1846. | Mean. 1845. | 1846. ; elie pete CECE 
Month. |3 Months. 
Jan. 0-48 | 0-59 | 0-51 | 0-53 : 1-00 | 0-48 
Feb. 0-70 | 0-64 | 0-92 | 0-75 : 0-54 | 0-92 
Mar. 0-35 | 0-43 | 0-80 | 0-53 c 0-80 | 0-59 
April | 0:77 | 0-53 | 0-80 | 0-70 B 1-00 | 0-59 
May 0-44 | 0-58 | 0-83 | 0-62 : 0-54 | 0-61 
June 0-40 | 0-34 | 0-88 | 0-54 L 0:37 
July 0-61 | 0-45 | 0-94 | 0-67 0-31 
Aug. || 0-70 | 0-76 | 1-34 | 0-93 \ 0-65 | 0-98 
Sept. 0-87 | 0-56 | 1-35 | 0-93 0-48 | 1-35 
Oct. 1-31 | 0-55 | 1-19 | 1-02 : 0-60 | 0-60 
Noy. || 0-40 | 1-05 | 0-91 | 0-79 : 1-14 | 0-71 
Dec. | 0-38 | 0-64 | 0-52 | 0-51 . 0-60 
11. The conclusions from this Table are :— 
1st, The daily mean declination departs farthest to the west of the monthly mean in August, September, 
and October, on the average about 0-96: the average departure for each three of the remaining nine months 
is nearly constant ; about 0760. 
* I have pointed out in a paper on the magnetic declination read before the Royal Society of Edinburgh, May 3, 1847, that the 
annual variation is inverted when the secular motion has an opposite sign. M. Anaco made an indistinct approximation to this fact 
in comparing the observations of CassINI with those of BowpiTcH (1810), Annales de Chimie, xvi., p. 66. M. Karmrz also alludes 
to the fact in comparing CassINt’s observations with observations by M. Kuprrer and M. Gauss (Kémtz Lehrbuch, iii., 426). In 
both cases the fewness of the latest observations are considered to render the conclusion doubtful. Dr Luoyp has recently distinctly 
stated the fact from the comparison of CAssINI’s observations with his own (Trans. Roy. Ir. Ac. xxii., May 1846). The following is 
from the abstract of my paper :—“ The annual period of magnetic declination consists of a double oscillation, having nearly the fol- 
“ lowing epochs of maxima and minima :— 
“ A max. Jan. 30. The min. April 30. The max. Sept. 10, A min. Dec. 10. 
« The author examines CassIni’s observations (1783-7). Although they confirm this law to some extent, it is not conceived that 
“ they can be trusted for such a determination. The author also verifies his result by grouping a large mass of modern observations. 
“ The observations at Washington [1840-42], and Toronto [1841-42], [discussed in the paper] with other facts, prove that the oscilla- 
« tion is inverted, when the secular motion of the needle has an opposite sign ; and Colonel Breauroy’s observations [1817-20] seem to 
« prove, that when the secular motion is zero, the annual period is a combination of the oscillations for a positive and negative secular 
“ motion.” (Proceedings Roy. Soc. Edin. May 1847.) 
