PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. 



327 



When we have hitherto considered the polar storms, the conditions of the horizontal intensity 

 have always been of the greatest importance, as the direction of the current-arrows was either pointing 

 eastwards or westwards. 



This is, however, not always the case as regards Kingua Fjord; on the contrary, it is in the decli- 

 nations that the strongest forces frequently are shown, and the direction of the current-arrows is very 

 frequently pointed pretty nearly due south. 



These somewhat peculiar conditions are surely connected with the northerly situation, as regards 

 magnetic conditions, of this station compared to the others with the exception of Fort Conger. 



We will here refer to the terrella experiments, which will be more fully dealt with in a sub- 

 sequent chapter. In order to elucidate the subject, we will however here give a copy of a photograph, 

 Fig. 140. 



Fig. 140. 



In most of the illustrations hitherto given, the terrella has been suspended on an axis, the position 

 of which has corresponded with that of the earth, thus forming an angle with the terrellas magnetic 

 axis of about 20. 



As this however gave a less easily seen representation of the entire polar area of precipitation, 

 the terrella is here suspended on an axis in the magnetic equatorial plane. The position of the electrode 

 can be thus altered as desired by turning the terrella on the axis on which it hangs and thus produce 

 some positions which should -correspond to various positions of the earth in relation to the sun. 



In the experiment corresponding with the three above given photographs, the cathode is placed in 

 the magnetic equator of the terrella and thus answers to the times when the direction from the earth to 

 the sun is perpendicular to the magnetic axis of the earth. 



On the first figure, the camera is pointed directly on the south pole of the terrella magnet, the 

 position of which on the plate is marked with a cross. The figures of light we here see represented, 

 should therefore correspond to the areas of precipitation which we would expect to find round the earth 

 magnetic north pole, or, more accurately expressed, about the intersecting point of the magnetic axis 

 with the northern hemisphere. The other picture is taken with the axis of the camera parallel to the 

 cathode-rays' direction of issue, so that the conditions should represent the areas of precipitation we find 

 on the night side of the earth. The third picture is meant to show the conditions around the earth 

 magnetic south pole, the photograph being taken directly towards the terrella magnet's north pole. The 

 position of this is also marked on the plate. 



