16 



CHANGES OF THE MAGNETIC DECLINATION 



Mean Monthly Curves of the Diurnal Changes of the Magnetic Declination at Van 



Rensselaer Harbor, 1854. 



And Simultaneous Mean Diurnal Variation at GREEN^^cH. 



4'' 



8 9 10 llMidn.l3 14 15 16 17 18 19 20 21 22 23 Noon 1 2 



4li 



The irregularities in the daily curves compared on succeeding days are very 

 considerable, as may be seen by glancing the eye over the last column of the pre- 

 ceding table, headed " daily means." No observations on account of disturbances 

 have been excluded from the table, and the following mean diurnal inequality, 

 therefore, contains their full effect. Comparing each hourly mean in the last 

 horizontal line of the above table with the general mean, the following figures 

 represent the resulting diurnal inequality of the declination during the first three 

 months of the year 1854. For the sake of comparison the diurnal inequality 

 observed at Greenwich during the same seventeen days has been made out and is 

 given in the last column. 



