66 Rev.W. Sidgreaves Magnetical Observations. [Feb. 9, 



sity X, the induction and temperature corrections have always been applied, 

 and the observed time of vibration has been corrected for the effect of tor- 

 sion of the suspending thread ; but no correction has been required for the 

 rate of the chronometer, or for the arc of vibration, the former having been 

 generally less than l s -0, and the latter less than 50'. 



A twist of the torsion circle through 90 has ordinarily deflected the 

 magnet through 10' of arc. 



In the calculations of the ratio ^, the third and subsequent terms of 



P O 



the series l+_ 2 +q+& c . have always been omitted. The value of the 



constant P was found to be 0'00219 ; this value being the mean of nine 

 determinations obtained each from two pairs of deflection observations at 



STONYHURST COLLEGE] 



Latitude 53 50' 40". Longitude West cJ 

 TABLE of the Results of the Monthly 



