OF THE EARTH’S MAGNETISM. 533 
maximum in December is as well shown at Toronto as at Makerstoun. The 
coincidence in these results, it appears to me, is quite remarkable. It is, indeed, 
to some extent accidental, since the errors of the observations are not only con- 
siderable (as an examination of the partial results will show), but the correc- 
tions for temperature employed in the reductions are very inaccurate.* 
50. I have computed the constants in the equation of sines for the mean of 
the eight years, and find (¢=0, Jan. 16)— 
X = 38-5301 +0:0008 sin (9+ 315°) + 0-0011 sin(20+185°); . . (4) 
or, putting the coefficient of the last term in ten-thousandths of X, it becomes— 
SInX 2d Uab ame Fe apmet et ee oat es Bre ace op) 
which gives the same epochs for the double maximum and minimum within 
three days as the Hobarton and Makerstoun results (§ 34), the coefficient being 
slightly greater. 
51. If we examine General SaBine’s means (1845-51) in a similar manner, we 
shall find— 
X =8-5309 + 0:0020 sin (0+ 313°) + 0-0010 sin (20+1559), . . (6) 
and the last term with the coefficient in ten-thousandths of X becomes— 
2°83 sin (264+155°). 4 ; ; ; ; F . ‘ (7). 
52. If we compare this also with the corresponding terms for Makerstoun and 
Hobarton, we shall find that the coefficient for Toronto has a value nearly equal 
to the mean of the two, and that the epochs of the double maximum and mini- 
mum at Toronto are within thirteen days of those at the two other places. 
53. Annual Period from Observations of Absolute Intensity, Cape of Good Hope. 
—The observations of absolute intensity made at the Cape of Good Hope are 
* T have taken the trouble to deduce the absolute force for the year 1845, the only year for 
which the data are in my possession, so as to eliminate the error due to the bifilar temperature 
coefficient. The following are the values in absolute measure from the Toronto volume, and 
according to my corrected computation :— 
Jan. | Feb. |March./April.| May. | June. | July. | Aug. | Sept. | Oct. | Nov. | Dec. 









minus 3°5370, 
Corrected by me, 
minus 3°5385, 
Toronto volume, 
0027 |-0022 |-0047 |-0025 |-0041 |.0093 |-0033 |-0035 |-0032 |-0042 |-0000 |-0031 


0025 |-0005 |-0035 |-0021 |-0049 |-0063 |-0056 |-0024 |-0011 |-0010 |-0000 |.0040 









The law is evidently to be traced even in these results; the greatest error of a monthly mean is that 
for July, =0:0038, or in ten-thousandths of X, =10-8. The errors are chiefly due to the difference 
between the mean temperature of the bifilar for the three days on which the absolute observations 
are made and for the month; in July, for example, this difference is 9°0 Fahr. 
