xliv Intkoduction to the Makeestoun Observations, 1844. 



the values of — , /)i, and qi, given above, and the values of r from the first column 



of Table 6, being substituted in this equation, the values of log tan u, column 12, 

 have been obtained. 



If Y, the vertical component, be substituted for X, in equation (2.), No. 34, we 

 shall have, since Y = X tan 6 



whence 



tan u 



k = 



n tan i 



where k is the value of -^^ for one micrometer division, u and n are the corrected 



horizontal and vertical deflections for the same distance )• ; the former in angular 

 measure, its logarithmic tangent being given, column 12, Table 6 ; and the latter in 

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

 zontal deflections ; 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 Jc, 13th column. Table 6 = 0-00000994. 



59. In the foot-notes to the observations, pages 1 to 157, the value of k is given 

 = 0-0000085, that having been the value deduced from the vertical deflections of the 

 balance needle compared with the horizontal deflections of a short unifilar magnet 

 •luly 1 and 2, 184G : when these vertical deflections are compared, by the previous 

 method, with the horizontal deflections of the same needle, given Table 7, 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 A 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. 



60. Adjustment of the balance needle. 



The balance needle was removed January 27* O*" 1844, for the purpose of deter- 

 mining its temperature coefficient by hot and cold water experiments : the details 

 of these observations have been already given. Introduction, 1841-2, p. xliii. : the 

 needle was readjusted January 27* S"". 



61. The observations before January 27* were connected with those after that 

 date in the following manner : — 



