OF THE EARTH’S MAGNETISM. 531 
that the curves thus formed agree wonderfully in their inflections—the increasing 
rapidity of diminution of force at the Cape being indicated by a descending 
curve; the increasing rapidity of increase at Toronto by an ascending curve; the 
slight differences at Trevandrum and Singapore are, I have no doubt, due to 
instrumental errors. 
42. On the whole, it seems probable that the monthly mean variations, inde- 
pendent of secular change, obey the same law. It does not appear from the 
curves last considered that the range of these variations is diminished near the 
equator, though the variations for Singapore are somewhat less marked than at 
the other places. If we take the variation of the monthly means from maximum 
to minimum and minimum to maximum for the years 1842-55 (see the projec- 
tions, Plate XXIV.) we find the range at Trevandrum and Singapore less than 
for higher latitudes. Thus— 
TABLE XIV.—RANGE OF ANNUAL PERIOD. 





eae Jan. to June to June to Jan. to 
April. April. | September. | September. 
Makerstoun, . . . 5°31 6:20 6-70 5:90 
Hobarton, . 2°). *: 4:30 4:40 6:00 5:90 
Munich; o>, Sa. 3°20 4:40 6°70 5:40 
Smgapore,;. y . 4:90 2°50 2°00 4°30 
Trevandrum, . . . 4:40 2-70 2°00 4:70 



43. These are the approximate variations; and were the Singapore and 
Trevandrum results as trustworthy as the others, we might conclude at once 
that the range was less in low than in high latitudes. We shall see afterwards 
the effect of disturbance on the daily means near the equator, already referred to 
as a cause for such a diminution. 
44. On account of the doubt as to the perfect accuracy of some of these 
results, I have not thought it necessary to compute the representative equations 
of sines. 
45. It is always desirable, when a law has been found differing from that 
obtained by others, that we should not only give good grounds for our own con- 
clusion, but, if possible, show the error or insufficiency of the one opposed to it. 
The only results with which I am acquainted, which it appears to me merit 
examination, are those obtained by General Saxnine from the observations of 
absolute horizontal intensity made at the Colonial observatories. 
46. These observations, it should be remarked, are affected by the error of 
VOL. XXII. PART III. 6x 
