OF THE EARTH’S MAGNETISM. 519 
13. The law of variation at both places is as follows :—The horizontal inten- 
sity diminishes in each year from February to March or April, and from June to 
July, August or September. It increases in the other months, the rate of increase 
being least rapid immediately before and after the diminution. This result is 
evidently a combination of the annual and secular variations. 
14. We should now proceed to the examination of the results for other obser- 
vatories. The series of observations at other places have unfortunately been so 
much broken up by accidental causes, spiders within the tropics, adjustments and 
changes of magnets everywhere, that observations for a moderate length of time, 
free from error, are not to be found. I have, however, taken much pains to deter- 
mine the coefficients,* and, if possible, the errors and their amounts for all the 
observations in my possession; the details of these corrections are given in the 
Appendix to this paper. The following tables contain the concluded corrected 
monthly means; they have been projected in Plate XXIII.; and the means in 
the last columns of each table in Plate XXIV. I have also projected the means 
of the Munich Observations 1843-5 in the same plate.+ I shall proceed first to 
examine the mode of variation of the monthly means at the different stations. 
TABLE VII.—MontTHiy MEAN VALUES OF THE HORIZONTAL INTENSITY (minus A 
OS) . 
10060 
CONSTANT) AT TORONTO, 1841-48. 1:00= 



1842. 1844. 


1843, 1845. 1846. 1847. 1848. 

Mon Tus, 






January. : : = did 17-84} 22°02} 50:10) 99-11 |132°85 |152-43 /152:23 
February, : ; é SoC BSOO HE. 50°86 |101:98 |132-00 |148-69 |153°47 
March, . . : : noe 7c ewe ee 48:25 |101:18 |129-76 |146-70 |154:09 
fepril,) : é : Rot Torte! Wa.- 47:62 |100:23 127-81 |144°38 |154:37 
May, ‘ 6 : : tek ZLB ie 54-71 |103°81 |126-47 |146-53 |157-63 
June, . : : : sks 20°54|  ... 64-83 |108-77 |129:41 |150°97 |161-21 
July, . : ; : Bee 12°93)/0 a. 72:00 /109-92 |131-48 |147-61| ... 
August, A 5 5 0-30) 17:05} ... | 77-66 |114-55 |132-77 |148-41 
September, . : : OT) Loh oye ks, 84-60 |118°60 |134-97 |145-64 
October, : : : 6°58] 16:06} ... 90:89 126-03 |138-31 |148-78 
November, : 5 : 10:34] 16-80} 44:09] 94:97 |130-11 |144-76 |147-79 
December, 21°49 100-05 |132:°64 |151-°69 |155-17 


















15. Toronto.—The observations were interrupted in February 1843, and when 
resumed after a new adjustment of the magnet in March, it was found that there 
Was an instrumental derangement which appeared to be removed on turning 
* See Bifilar Magnetometer, Trans. Royal Soc. Ed. vol. xxii. p. 467. 
+ Resultate des Mag. Obser. in Miinchen, 18438-4—5. See also Makerstoun Observations, 1844, 
p- 357 (foot-note) ; and General Results (Trans, Royal Soc. Edin., Vol. xix., part ii.) p. xxxiii. 
For convenience of comparison, I shall repeat here the quantities projected in Plate XXIV, and to be 
found in the works cited :— 
Jan. Feb, March. April. May. June. July Aug. Sept. Oct. Nov. Dec. 
—0:29 —0:86 —0:29 —1:58 +265 +2:38 +42: "80 +1:36 ~ 4-91 —3:28 —0:45 41-72 
VOL. XXII. PART III. 6s 
