XIV 
Geneeal Results of the Makeestoun Obseevations. 
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 cokimns 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, vi^ith their DitFerences. 
Month. 
Mean Westerly Departures. 
Mean Easterly Departures. 
Diff. of 
Mean 
1844. 
1845. 
1846. 
Mean. 
1844. 
1845. 
1846. 
Mean. 
Depart. 
Jan. 
0-48 
0-59 
0-51 
0-53 
0.69 
1-00 
0-48 
0-72 
-0-29 
Feb. 
0-70 
0-64 
0-92 
0-75 
0-75 
0-54 
0-92 
0-74 
+ 0-01 
Mar. 
0-35 
0-43 
0-80 
0-53 
0-41 
0-80 
0-59 
0-60 
-0-07 
April 
0-77 
0-53 
0-80 
0-70 
0-41 
1-00 
0-59 
0-67 
+ 0-03 
May 
0-44 
0-58 
0-83 
0-62 
0-65 
0-54 
0-61 
0-60 
+ 0-02 
June 
0.40 
0-34 
0-88 
0-54 
0-37 
0-37 
0-88 
0-54 
0-00 
July 
0-61 
0-45 
0-94 
0-67 
0-49 
0-31 
0-87 
0-56 
+ 0-11 
Aug. 
0-70 
0-76 
1-34 
0-93 
0-41 
0-65 
0-98 
0-68 
+ 0-25 
Sept. 
■ 0-87 
0-56 
1-35 
0-93 
0-58 
0-48 
1-35 
0-80 
4-0-13 
Oct. 
1-31 
0-55 
1-19 
1-02 
0-66 
0-60 
0-60 
0-62 
-t-0-40 
Nov. 
0-40 
1-05 
0-91 
0-79 
0-63 
114 
0-71 
0-83 
-0-04 
Dec. 
0-38 
0-64 
0-52 
0-51 
0-72 
0-60 
0-65 
0-66 
-0-15 : 
Mean Departures, ■without reference to 
Direction. 
1844. 
1845. 
1846. 
Means of each 
Month. 
3 Month 
0-56 
0-74 
0-49 
0-60 
0-64 
0-72 
0-59 
0-92 
0-74 
0-63 
0-38 
0-56 
0-68 
0-54 
0-64 
0-53 
0-70 
0-68 
0-64 
0-59 
0-53 
0-56 
0-70 
0-60 
0-59 
0-38 
0-35 
0-SS 
0-54 
0-58 
0-54 
0-37 
0-90 
0-60 
0-64 
0-52 
0-70 
M3 
0-78 
0-75 
0-70 
0-52 
1-35 
0-S6 
080 
0-87 
0-58 
0-79 
0-75 
0-SO 
0-49 
1-09 
0-SO 
0-79 
0-70 
0-50 
0-62 
0-58 
0-57 
0-60 
11. The conclusions from this Table are : — ■ 
\st, The daily mean declination departs farthest to the west of the monthly mean in August, September, i 
and October, on the average about 0'*96 : the average departure for each three of the remaining nine mouths ' 
is nearly constant ; about 0'-60. \ 
* 1 have pointed out in a paper on the magnetic declination read hefore the Royal Society of Edinburgh, ^fay 3, 1847, that the | 
annual variation is inverted when the secular motion has an opposite sign. M. Aeago made an indistinct approximation to this fcct | 
in comparing the observations of Cassini with those of Bowditch (1810), AnnaUs dc Chimie, xvi., p. 66. M. Kaemtz also alludes j 
to the fact in comparing Cassini's observations with observations by M. Kupffer and M. Gauss (Kiimt: Lchrbuch, iii., 426). In I 
both cases the fewness of the latest observations are considered to render the conclusion doubtful. Dr Lloyd has recentlv distinctly , 
stated the fact from the comparison of Cassini's observations with his own (Trans. i?oy. Jr. Ac. xxii.. May 18461. The following is | 
from the abstract of my paper : — " The annual period of magnetic declination consist* of a double oscillation, having nearly the fol- 
" lowing epochs of maxima and minima : — 
" A max. Jan. 30. The min. April 30. Tl\e max. Sept. 10. A min. Dee. 10. 
" The author examines Cassini's observations (17S3-7'). Although tbov confirm t)iis law to some extent, it is not conceived tildt 
" they can bo trusted for such a determination. The author also verities liis result by grouping a largo mass of modern observations. 
" The observations at Washington [1840-42], and Toronto [1841-42], [discussed in tlie paper] with other facts, prove that theoscill*- 
" tion is inverted, wlien the secular motion of the needle has an opposite sign ; and Colonel Bem'fov's observations [1S17-20] seem to 
" prove, that when the secular n\otion is zero, the annual period is a combination of the oscillations for a positive and negative secular 
" motion." (Procccdinos lioij. Soc. IaHu. Jlav 1847.) 
