322 



BIKKELANI). THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



at the other polar stations, whereas the agreement in the horizontal elements is very close. In Sodan- 

 kyla too, the perturbing forces taken from the observations of vertical intensity, are often apparently 

 abnormal compared with the conditions at the stations situated in the vicinity of that station. 



As stated in Art. 23 the map-projection employed for our polar chart is not orthomorphic. The 

 deformation is not great, however, but yet sufficiently so, especially at the southern stations, to be taken 

 into consideration in the placing of the current-arrows. These are thus not placed at the angle which 

 they form on the earth with for instance the geographical east and west, but at a rather smaller angle. 

 The amount by which this angle (v) is reduced has been calculated for two or three latitudes, the result 

 being given in the following table : 



TABLE XLIX. 



In these charts also we have indicated the position of the sun and the moon. Their signs (Q and 

 ) are placed in the margin of the chart, that for the sun on the noon meridian, that for the moon on 

 the meridian that it is crossing at the moment under consideration. The point in which the magnetic 

 axis intersects the surface of the earth, has been calculated for the beginning of 1883 as situated in lati- 

 tude 782o'N., and longitude 6849'W('). 



In the preceding observations, Greenwich mean time has been employed throughout, and it will also 

 be used now in order to facilitate comparison. 



In the observations of which we make use, everything relating to the fixed days is given ac- 

 cording to Gottingen mean time, and we have therefore effected the necessary reduction all through. 

 The difference in time between these two places amounts to o h 39 m , 8, or in round numbers to o h 4O m , 







the latter being the figure we have employed. Lastly, the hours, as before, are counted from o to 24, 

 12 answering to Greenwich mean noon. 



With regard to the arrangement of the perturbations, we have used the same method as previ- 

 ously; first treating of the days on which the simplest and most perspicuous conditions of perturbation 

 prevail those on which the typical phenomena are most prominent. The more complicated phenomena 

 are dealt with later. 



Amongst the disturbances we find here, is also an equatorial one, but, as it is the polar distur- 

 bances that interest us most, this perturbation is noticed amongst the last. 



The plates of the curves are, on the other hand, arranged in chronologic order. 



In conclusion, we give a table of the perturbations in the order in which they are described. 



(') V. Carlheim Gyllenskold, "Note sur le Potentiel Magnetique de la Terre exprime en Fonction du Temps". Arkiv for 

 matematik, astronomi och fysik. Vol. 3, No. 7. Upsala 1906. 



