xlvi Introduction to the Makeestoun 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. 2c?, That the value of q' 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. 





Sum of 







Sum of 





Period. 



Diff. 



Value of 



Period. 



Diff. 



Value of 





Temp. 



</- 





Temp. 



'/■ 



1844. 



o 



Si-. Hiv. 



1845. 







Sc. Div. 



May 9— May 24 



320-6 



2-22 



Jan. 13— Feb. 12 



1809-0 



1-81 



May 29— June 28 



1610-7 



1-83 



Feb. 26— Mar. 28 



1608-1 



2-06 



July 17— July 30 



270-0 



1-77 



June 2 — July 2 



1725-0 



2-13 



Sept. 2— Sept. 25 



1164-4 



1-96 



Dec. 8— Deci 31 



757-7 



1-65 



Nov. 26— Dec. 13 



833-3 



1-99 









The series of observations for 1844, giving each result an equal weight, give q' = 1-95 sc. div. 



1845, q' = 1-91 - 



■ 1844, giving the results the weights 2 A ^, give g" = 1-92 ••• 



1845, q' ^ 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 a t^^ we find 



q' = 1-93 sc. div. 



The adopted value of the temperature coefficient of the bifilar magnet, 

 q' = 1*90 sc. div. 



The value of one scale division in parts of force for the period of comparisons 

 (1844 and 1845), being k = 0*000140. 



Whence, the correction for 1° Fahr., from comparisons of observations, ia q = 0-000266. 

 * See foot-note, p. 39.5 of the volume for 1844. 



