Temperature Coefficient of the Balance Magnet. 



xlix 



occur at the same time with the greatest variations of mean temperature ; it is 

 believed that it is to this cause chiefly that the differences of the results are to be 

 attributed. 



Table 8. — Determinations of the Temperature Coefficient of the Balance Magnet. 





Sum of 







Sum of 





Period. 



Diff. 



Value of 



Period. 



Diff. 



Value of 





Temp. 



<l- 





Temp. 



<l- 



1843. 



o 



Mic. Div. 



1844. 



o 



Mic. Div. 



Jan. 16— Jan. 21 



58-4 



8-21 



Nov. 4 — Nov. 30 



1066-2 



6-92 



Jan. 23— Jan. 28 



90-9 



6-99 



Dec. 2— Dec. 28 



939-0 



7-20 



Jan. 30— Feb. 4 



640 



7-21 



1845. 







Feb. 6— Feb. 11 



67-8 



6-69 



Jan. 6— Feb. 8 



2086-3 



7-57 



June 1 — June 30 



1885-8 



7-82 



Feb. 26— Mar. 28 



1830-1 



8-00 



Sept. 6— Sept. 16 



120-4 



8-04 



Apr. 10 — May 10 



1279-1 



9-08 



1844. 







June 2 — June 30 



1551-6 



8-47 



Jan. 1— Jan. 26 



971-4 



9-27 



July 7 — Aug. 6 



1069-8 



10-01 



Feb. 5— Mar. 6 



1392-5 



9-30 



Sept. 9— Oct. 13 



1580-6 



7-81 



May 9— May 24 



350-6 



7-93 



Dec. 11— Jan. 10 



1585-2 



10-17 



May 29— June 29 



1693-1 



7-43 



1846. 







July 4 — Aug. 3 



1360-9 



1-1^ 



Nov. 30— Dec. 26 



1190-2 



7-72 



Aug. 4— Sept. 6 



904-0 



7-90 









Giving the differences for all the series equal values, and dividing the sums of 

 differences of the daily means in micrometer divisions by the sums of differences of 

 the daily mean temperatures of the needle, we have 



q' - 8-23 mic. div. ; 

 but if the results from the bad series for July 7 — August 6, 1845, and December 

 10, 1845 — January 10, 1846, be rejected, the value would be 



cl = 7-99 mic. div. 



If the whole series were properly weighted, it is believed that the resulting value 

 of q' would be less than 8-00 mic. div. The excellent series, November 30 — De- 

 cember 26, 1846 (after an adjustment July 1846) gives 



q' = 7'12 mic. div. 

 The adopted value of the temperature coefficient for the balance magnet = 7'90 mic. div. 

 It is believed that this value, which has been used in correcting all the observations 

 since the commencement of 1843, is within one-tenth of a division of the truth. 



81. The following matters should be attended to in determining the tempera- 

 ture coefficient by the previous method. 



1st, The period selected should be free from considerable magnetic irregularities. 



2c?, There should be a considerable change of daily mean temperature, the tem- 

 perature at the beginning and end of the period being nearly the same. 



3d, The smaller the duration of the period consistently with the 2d the better. 



ith, It will be found best, in general, to correct the daily means at first by an 

 approximate coefficient, and 



MAG. AND MET. OBS., 1845 AND 1846. 



n 



