xlii Introduction to the Makerstoun Observations, 1845 and 1846. 



measure, its logarithmic tangent being given, column 12, Table 5 ; and the latter in 

 micrometer divisions, reduced to the temperature of the deflecting bar during hori- 

 zontal deflections ; 6 is the magnetic dip, the adopted value being 71° 20'. The 

 temperature coefficient of the deflecting bar = 0-000285. 



The mean of all the values of k, 13th column, Table 5 = 0-00000994. 



60. When the vertical deflections of the balance needle made July 1^ and 2^ 

 1846, are compared by the previous method, with the horizontal deflections of the 

 same needle, given Table 6, allowance being made for the loss of magnetism of the 

 deflecting bar between July 1846 and January 1848, k is found = 0*00001025. 



The adopted value of k for the balance magnet=0-0000100 



This value of one micrometer division in parts of the whole vertical component 

 may be considered applicable to all the observations of the balance magnet since 

 1841 : it has been used in the abstracts of results for the present volume. 



61. The balance needle was deflected July 1 and 2, 1846, for the purpose of de- 

 termining the value of k, it was readjusted on July 2^. 



As the readings of the micrometer had become previously too much negative, 

 the horizontal screw was turned in a little, the following comparisons of observations 

 before and after the adjustment were made for the purpose of connecting the two 

 series. 



Mean balance reading corrected for temperature, June 29^ and 30*^ 

 July 3d and 4^ 



Difference of readings before and after adjustment, .... 



Mean balance reading corrected for temperature, June 1* — 13*^, . 

 ■ JunelS-i— 27^ . 



Afic. Div. 



= 3830 

 = 957-0 



= 574-0 



= 396-5 

 = 396-0 



= - 0-5 



Mean change of reading for 14 days, 



Mean reading, therefore, before adjustment, corresponding to July 1^^, . . . = 3956 



Mic. Div. 



Mean balance reading corrected for temperature July 6^ — 18**, = 966-4 

 July20d— Aug. 1\ =957-5 



Mean change of reading for 14 days, = — 8*9 



Mean reading, therefore, after adjustment, corresponding to July 11*^, . . . = 9731 



The readings after adjustment are therefore greater than before adjustment, by 577-5 



A comparison of the mean for the fortnight before adjustment, with that for the 

 fortnight after adjustment, rejecting days of disturbance, and allowing for secular 

 change, gave 577. 



Mic. Div. 



The readings after adjustment, are therefore considered greater than those "i ^-^ « 

 before adjustment, by J 



