354 



SCIENTIFIC RESULTS OF Z1EGLER POLAR EXPEDITION 



REDUCTIONS FROM DECLINATION OBSERVATIONS AT ALGER ISLAND 



DIURNAL VARIATION 



In deriving an expression representing the diurnal variation in magnetic declination over 

 the period of observation at Alger Island the same methods have been used as in the case of 

 the Teplitz Bay series (see pages 275 to 294). A tabulation of the resulting mean magnetic 

 declinations as deduced from the observations between June 26 and July 31, 1905, is given on 

 the following page. 



The analytical expression representing the daily variation of the east declination of the 

 needle as deduced from these means is 



Z?=20 28/4 + 34/70 sin (# + 3 15') + n. '55 sin (20+292 31') 

 + 7. '94 sin (3 #+232 25') + 1/73 sin (4 0+150 43') 0/65,* 



the angle f> counting from 15 as 0.5 hour A. M. A graphical representation to scale of this 

 formula, together with the mean values from which it is deduced, is given in figure 23. The 

 agreement between the individual observed means and values computed for the corresponding 

 times is given in the following summary, in which the observed and computed values are repre- 

 sented by letters O and C respectively, easterly deviation from the mean value for the whole 

 period being indicated by a plus sign, and vice versa, and extremes being in bold-face type. 



Summary of observed and computed diurnal variation of magnetic declination at Alger 

 Island for period fune 26 to July 31, 1905 



For a value of magnetic declination at Alger Island, practically referring to mean of day f 

 the mean of the tabulated observational means may be taken, viz : 



20 26V4 E for the epoch 1905.53. 



* This quantity is the probable error of a single representation. 



