xlvi_ INrRopUCTION TO THE MAKERSTOUN OBSERVATIONS, 1845 AND 1846. 
sons have been obtained, whether it has been obtained from comparisons of daily 
means, at 1, or 2, or 3, . . . . or 14 days’ interval. 
71. 2d, That the value of g’ is the same, whether the differences of temperature 
have been due to natural or artificial causes, and when the differences of temperature 
of the magnet have had an opposite sign from those for the temperature of the ex- 
ternal air. 
72. From the second result, it follows, that the variations of the horizontal 
component of the earth’s magnetism are wholly independent of the temperature of 
the air, and from both results it appears probable that they are independent of the 
temperature of the soil.* . 
73. The following Table contains the sums of differences of the daily mean 
temperature of the bifilar magnet, and the value of ¢/ which has resulted from each 
series of comparisons. The series of comparisons for 1845 have been made since 
the publication of the series for 1844, for the purpose of verifying the constancy of 
the result. 
TABLE 7.—Determinations of the Temperature Coefficient of the Bifilar Magnet. 
Period. iff. bs of Period. iff. 7 of 
1844. Se. Div. 1845. 
May 9—May 24 2-22 | Jan. 13—Feb. 12 
May 29—June 28 1:83 | Feb. 26—Mar. 28 
July 17—July 30 : 1-77 June 2—July 2 
Sept. 2—Sept. 25 1-96 Dec. 8—Dee: 31 
Nov. 26—Dee. 13 1.99 
Robe cn oupenctensicicwasce ceeanee snes Seam ax= 1845, Eder aot een ateer bap et mapgates sie cos icic + spssellosicwts g — 191 
tenets seen eeeenecenscneeseeereeteneaeeee 1844, giving the results the weights TAZ, give Gee 
ectrvaterststetsosssebcntars ceneanedass 1845, seseecesscteeeeeeseerseeteeseeceseseetseesstereeees gf = 1:95 
Whether the results for each year have equal weights, or have weights depend- 
ing on the sums of differences of the daily mean temperatures (2 4 ¢), we find 
7 = 1:98 se. div. 
The adopted value of the temperature coefficient of the bifilar magnet, 
g = 1°90 se. div. 
The value of one scale division in parts of force for the period of comparisons 
(1844 and 1845), being & = 0-000140. 
Whence, the correction for 1° Fahr., from comparisons of observations, is gq = 0000266. 
* See foot-note, p. 395 of the volume for 1844. 
