MAGNETIC OBSERVATIONS 9 



The observations are arranged so that two sets of deflections come between two sets of 

 oscillations, and t and t' do not usually differ very much. Consequently an erroneous value 

 of q has little effect on the resulting value of horizontal intensity. 



To determine the effect of the steel tacks on declinations as observed we have the following 

 declination observations at the Cheltenham Magnetic Observatory : 



O) Before removal of tacks, by W. J. Peters : 



Date Declination 



1905 west 



o / 



September 19 5 18.6 



September 20 20.0 



September 20 19.2 



September 21 18.7 



September 21 18.9 



September 22 19.8 



September 22 17.2 



Mean 5 18.9 



(V) After removal of tacks, by W. F. Wallis 



Date Declination 



1 905 west 



o / 



October 27 5 18.5 



October 27 18.7 



October 28 18.9 



Mean 5 r8.7 



The results by the Observatory magnetometer No. 26 were : 



Date Declination 



1 905 west 



O I 



September 5 18.7 



October 5 18.9 



All the above observations have been corrected for diurnal variation. They show that for 

 declinations determined with Magnetometer No. IIII no correction is required. 



To determine the effect of the steel tacks in horizontal intensity observations we have the 

 following results at the Cheltenham Magnetic Observatory : 



(a) Before removal of tacks, by W. J. Peters : 



Date Horizontal 



1905 intensity 



r 



September 20 19809 



September 21 20 



September 22 n 



Mean 19813 



