OF THE OBSERVATORY OF CAMBRIDGE BY GALVANIC SIGNALS. 



513 



instrument, the constant excess of the former was found to be - 2",65, for the position of the 

 instrument in which the lamp for illuminating the field of view is westward. In the 

 subjoined table £ 2 is the value of £, which would be given by levelling with the spirit-level, 

 and (£ - £j) + (^ - £ 2 ) or £ - £ 2 is the quantity required for calculating the effect of the 

 forms of the pivots on the observations of transits. 



On April 4 and April 6 the measures for finding the value of £ were taken for intervals 

 of 5° of zenith distance. It is unnecessary to state here in more detail the calculations by 

 which the corrections for the forms of the pivots were obtained, as a full account will appear 

 in the published Cambridge Observations. The quantities actually employed for the 

 correction of those transits that were taken for the determination of the longitude are 

 contained in the following list : — 



Zen. Dist. 

 South. 



Correction. 



Zen. Dist. 

 South. 



Correction. 



Zen. Dist. 

 South. 



Correction. 



+ 90° + 0,44 



85 +0,41 



80 + 0,41 



75 +0,40 



70 +0,40 



65 + 0,40 



60° +0,36 



+ 55 + 0,34 



50 +0,28 



45 +0,24 



40 +0,25 



35 + 0,30 



30° + 0,32 



25 +0,35 



+ 20 +0,32 



- 36° . 19' 

 Polaris 



- 39°. 15 

 Polaris SP 



J... +0,i 



66—2 



