MAGNETIC OBSERVATIONS 



295 



CHARACTERISTICS OF DIURNAL VARIATION IN MAGNETIC DECLINATION AT TEPI.ITZ BAY 



The characteristic features of the curves, figures 5 to 19, representing the total diurnal 

 variation in magnetic declination for the various periods discussed are summarized in the 

 tabulation following. In this summary a plus sign denotes a departure to the east of the mean 

 value, while a negative sign denotes a departure to the west of the mean value. The epochs 

 of mean declination are designated I and II, the former being the passage of mean in course 

 of westward movement, and the latter in course of eastward movement of the needle. 



* For these intervals the secondary phases, while indicated, have their crests no longer definitely marked. 



From the above it at once appears that the principal maximum and minimum of east decli - 

 nation occur at earlier and later times respectively than for stations in lower latitudes. The 

 morning extreme is reached almost always between 5 and 6 o'clock. The afternoon extreme 

 varies between 6 and 10 o'clock without any very systematic cycle dependent upon the 

 chronological order of the periods ; in the half-yearly means, however, it is earlier for the 

 winter season than for the summer season by about one hour. The increase in diurnal range 



