DECENNIAL PERIOD OF MAGNETIC VARIATIONS, ETC. 567 
TABLE I1.— Yearly Means of the Ranges of Monthly Mean Diwrnal Variations of the Magnetic 
Declination corresponding to the 1st of each month.—Trevandrum, 1853-1875. 


























Year. Jan. Feb. Mar. | April. | May. | June. | July. | Aug. | Sept. Oct. Noy. Dee. 
eee ee ce iea | 2.6 | 204) 959.| 947 | 2.50! 2.54 
1854 | 2-50 | 2-45 | 2.38 | 2-29 | 2-31 | 2-32 | 2-31 | 2-80 | 2-30 | 2-31 | 2.33 | 2-30 
1855 | 2-28 | 2-27 | 2.26 | 2-26 | 2-25 | 2-19 | 2-11 | 2:09 | 2.07 | 2:09 | 2.03 | 1-96 
1856) 1-93 | 1:93 | 1-93 | 1-88 | 1-88 | 1-93 | 2-01 | 2-00} 2-02 | 2-03 | 2-03 | 2-12 
1857 | 2-11 | 2-10} 2-10 | 2-18 | 2-18 | 2.14] 2-14 | 2-19 | 2-18 | 2-21 | 2-26 | 2.24 
1858 | 2-29 | 2:36 | 2-41 | 2-33 | 2-34 | 2.42 | 2-41 | 2-40 | 2-41 | 2.39 | 2.39 | 2.42 
1859 | 2.47 | 2-47 | 2.46 | 2.53 | 2.58 | 2-57 | 2-65 |. 2-69 | 2-72 | 2-78 | 2-80 | 2.82 
1860 | 2-84 | 2-83 | 2-98 | 2-96 | 2-97 | 2.96 | 2-89 | 2-81 | 2-73 | 2-66 | 2-58 | 2.51 
1861 | 2-49 | 2-49 | 2.43 | 2.44 | 2-42 | 2.88 | 2-41 | 2-45 | 2-47 | 2-48 | 2-50 | 2-50 
1862 | 2.50 | 2-44 | 2.31 | 2-24 | 2.22 | 2.25 | 2.26 | 2-28 | 2-30 | 2-30 | 2-29 | 2.31 
1863 | 2-27 | 2-33 | 2:36 | 2-33 | 2-34 | 2:32 | 2-29 | 2.25 | 2-26 | 2-22 | 2.22 | 2.23 
1864 | 2.26 | 2-21 | 2.25 | 2.32 | 2-32 |] 2-28 | 2-29 | 2.32 | 2-35 | 2-38 | 2.42 | 2.39 
1865 | 2-37 | 3-34 | 2.29 | 2.23 | 2-24 | 2-26 | 2-22 | 2-15 | 2-17 | 2-16 | 2-11 | 2-06 
1866 | 2-04 | 2-00 | 1-95 ; 1-92 | 1-91 | 1-92 | 1-94 | 1-93 | 1-90 | 1-91 | 1-95 | 1-96 
1867 | 1-95 | 1-99 | 2-03 | 1-97 | 1-98 | 1-99 | 1-97 | 2-00 | 2-01 | 2-03 | 2.04 | 2.07 
Becsni2- il | 2-08 | 2:15 | 2-25 | 2:99 | 2-91 | 9-96 | 9:39 | 2-44 | 9.49 | 9:39 | 9.44 
1869 | 2-51 | 2-63 | 2-66 | 2-65 | 2-69 | 2-72 | 2-68 | 2-58 | 2-51 | 2-53 | 2-53 | 2-52 
1870 | 2-55 | 2-60 | 2-69 | 2.79 | 2-75 | 2-72 | 2-74 | 2-79 | 2-87 | 2.85 | 2.92 | 2.91 
1871 | 2-88 | 2-86 | 2-83 | 2-78 | 2-81 | 2-84 | 2-89 | 2-86 | 2-86 | 2-85 | 2-81 | 2.85 
1872 | 2-80 | 2-77 | 2-71 | 2-76 | 2-73 | 2-73 | 2-68 | 2-67 | 2-64 | 2-65 | 2.59 | 2.57 
18%3 | 2-53 | 2-52 | 2-50 | 2.43 | 2-43 | 2-36 | 2-31 | 2-28 | 2-31 | 2.34 | 2-37 | 2.31 
1874 | 2-29 | 2-187} 2-11 | 2-10 | 2-10 | 2-09 | 2-12 | 2-10 | 2-07 | 2-07 | 1-97 | 2-01 
1875 | 2-01 | 2:00 |} 2-00 | 1-99 | 2-00 | 2-00 | 1-95 | 1-94 | 1-94 | 1-93 | 1-95 | 1.93 
10. The earliest systematic series of observations of the magnetic declination 
showing a maximum or minimum of diurnal range are those of Cassrnt (Paris, 
1784-88),* Gitpin (London, 1786-1805),t BEauroy (London, 1813-20),t and 
Araco (Paris, 1820-30).§ Of the later series I have employed the observa- 
tions of Gauss (Géttingen, 1834—41),|| Lamonr (Munich, 1840-50),1 Luoyp 
(Dublin, 1840-50),** Broun, (Makerstoun, 1842-46),tt YouncuusBanp and 
* De la déclinaison et des variations de l’Aguille aimantée, Paris, 1791. 
+ Phil. Trans. 1806, p. 416. 
¢{ Txomson’s Annals of Philosophy. 
§ Cuvres de F. Araco, t. iv p. 501. 
|| Resultate des Mag. Vereins im Jahre 1836, 1839. 
{7 Resultate d. Mag. Beob. 1840-42; Result. d. Mag. Observatoriums in Miinchen, 1843-45; Poa- 
crnporFr Annalen, B. 84. In obtaining the yearly mean range, 11 has been added to the yearly 
means from 1841.1 (Feb. 1), to 1842-0, derived from two-hourly observations, to reduce to the means 
from 1842°0 to 1845°5 from hourly observations, after 1845°5, 06 is added. The object of these 
corrections has been to obtain comparative results from different places for the epochs of minimum 
37). 
é ‘es Observations made at the Mag. and Met. Obs. Dublin, vol. i. p. 89; vol. ii. p. 53, The ranges 
are taken from observations at 7 a.m. 1 P.M. or src) P.M, in 1840-43, and from the three-hourly 

observations after 7 a.m. in the following years. 
+t Observations in Magnetism and Meteorology (Trans. Roy. Socy. Edin. vol. xvii., xviii, and xix.), 
1-2 has been added to the yearly mean ranges fron January 1, 1843, to June 1, 1844. 
VOL. XXVII. PART IV. 7 it 
