MAGNETIC OBSERVATIONS 



295 



Characteristics of Diurnai< Variation in Magnetic Decmnation at Tepwtz 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. 



Period 



1903-1904 



July (interpolated) 



August (interpolated) 



September (interpolated) . ■ ■ ■ 



October 4 to October 30 



Noyember i to November 28 . . . 

 November 29 to December 26 . . 



December 27 to January 23 



January 24 to February 20 



February 21 to March 19 



March 20 to April 16 



April 17 to May 14 



May 15 to June 11 



June 12 to July i 



Summer mean — Oct. to March. 

 Winter mean— April to Sept. . 

 Mean of year. ■ 



Secondary phase 



Maximum 



Iv.M.T. 



16.8 



17-4 

 17.0 

 16.4 

 14.2 



14-3 

 18.7 

 17.7 

 18.6 

 20.0 



16.7 



Am't 



L.M.T. 



-8.7 



- 3-9 

 -3-8 

 -54 



- 2.7 



- 2.0 



- 2.2 



-19. 1 



-15-7 



-24-5 

 * 



- 9.2 



Minimum 



* 



* 



143 

 13-8 

 13-5 

 12.5 



II. o 

 II. o 



151 

 15-5 

 16.0 



17-3 



* 



14.2 



* 



Am't 



K 



-11.8 

 -II. 1 

 -16.3 

 -10. 1 



-13-3 

 -13.0 



- 9.1 

 -21.2 

 -21.2 

 -26.8 



» 



- 7-4 

 » 



* 



3-1 

 7.2 



12.5 



4-7 



10.6 



II. o 



6.9 

 2.1 



5-5 

 2-3 



* 

 1.8 



Bpochs 

 of mean 

 declina- 

 tion 



h 

 12.8 



12.0 



11. 



9.8 



8.4 

 9.6 

 8.8 

 8.9 

 10.5 



10. 1 



9-9 

 12.9 

 12.8 

 II. 6 



9.2 

 10.2 





II 



h 

 1-5 



1.2 

 0.2 



0.3 

 b.6 



22.9 

 0.4 



23.8 

 o.i 

 0.0 

 0.7 

 0.9 

 1.2 

 1.2 



23.8 

 0.5 



*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 



