574 filRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903. 



We distinctly see the shape of the precipitation upon the vertical screen, answering to a magne- 

 tisation of 14 amperes. The lowest curved edge of the precipitation upon the west side of the vertical 

 screen lies higher than the uppermost edge of the precipitation upon the east side of the screen. For 

 the sake of comparison we would observe that in photographs 7, 8 and 910 which we shall return 

 later the precipitations are seen with very low magnetisation, namely 6.5 amperes. 



In the above-mentioned experiment with 14 amperes to the terrella, it was ascertained that 

 precipitation B upon the horizontal screen, had disappeared in the position given to the vertical screen 

 of an hour-angle of 190, but the western part of precipitation B appeared when the vertical screen was 

 turned 15 or 20 either west or east. This shows that the cathode rays which produced this part of 

 precipitation B, were stopped by the vertical screen in the position shown in the photograph, but that 

 the rays slipped past and descended upon the horizontal screen as soon as the vertical screen was turned 

 a little. It still appeared that if the vertical screen were turned eastwards to an hour-angle of about 230, 

 the luminous line of precipitation bounding the easternmost part of precipitation B upon the horizontal 

 screen, also made its appearance. 



Photographs 5 and 6 were taken from an experiment with a pressure of o.ooi mm., 14 amperes 

 to the terrella, 3200 volts tension, and 19 milliamperes to the discharge-tube. The vertical screen has 

 an hour-angle of 240, and the photographs are taken from positions with hour-angles of 310 and 90. 



The rays here are fairly stiff, but the westernmost part of precipitation B is seen sufficiently 

 clearly, while the easternmost has not come out distinctly in the photograph. 



Experiments were made with 8 and 24 amperes to the terrella. With low magnetising 8 amperes 

 - the precipitation on the day-side (that turned towards the cathode) of the vertical screen was of great 

 extent when the screen had an hour-angle of, for instance, about 200 (or 180 less, see, for example, 

 Nos. 7 9 of fig. 209). On turning the screen eastwards, so that the angle became greater, the preci- 

 pitation moved out; but there was still a little left on the uppermost right corner of the screen, look- 

 ing from the cathode, right until an hour-angle of 260 had been reached (see No. 5). 



With a magnetisation of 24 amperes, the precipitation was always far out on the screen, and had 

 already disappeared with a turning of the screen to an hour-angle of 220. 



When the terrella was turned so that the vertical screen had an hour-angle of about 225, all 

 precipitation of light disappeared from the day-side of the screen when the magnetisation was 14 amperes, 

 and did not return to that side until the screen had been turned about 135 farther, i. e. when the 

 hour-angle of the screen was about 360, and the former night-side was about to become the day-side. 

 It was otherwise with the night-side of the screen. There was at first no light there either, when the 

 light had disappeared from the day-side, with an hour-angle of 225; but after turning the screen 75, 

 there was the maximum of a faint precipitation upon the night-side on the wing of the screen in which 

 was the hole, and which then had an hour-angle of 300. This precipitation is closely connected with 

 the small, faint half-ring of light that passes through the pole (see fig. 134 and p. 298 in Section I). 



Further experiments were made for the purpose of explaining precipitation B upon the horizontal 

 screen, when employing 8 amperes to the terrella. It was observed that precipitation B originated in 

 rays which, if the vertical screen were in a suitable position (an hour-angle of about 15) and caught 

 them, fell near the lowest, curved border of the precipitation of light. Precipitation B could be partly 

 or entirely removed from the north side of the horizontal screen, by adjusting the vertical screen in a 

 suitable manner. At the same time, as was to be expected, the corresponding precipitation B on the 

 south side of the horizontal screen was in all cases unchanged and just as bright, as there was no 

 vertical screen in the south polar regions. 



It should be remarked that while the terrella was being turned, a distinct shadow of the right edge 

 (looking from the cathode) of the vertical screen often appeared in precipitation A upon the north side 



