PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 403 



area of divergence of the positive system of precipitation. The effects of the two systems will pre- 

 sumably be combined here, as they will each produce an arrow with a southerly direction. 



On the next four charts, VII to Xfrom 20'' 50'" to 21'' 2j m , we find the perturbation-conditions 

 represented as they appear at the time when there are powerful negative storms round the auroral zone. 

 The form of the field of perturbation undergoes no particular change, but from time to time there is some 

 variation in the strength. 



The current-arrows at the European stations are directed southwards, as they usually are in the polar 

 night-storms. This circumstance is certainly in some measure due to the more western positive system; 

 for in the district in which it appears, this storm will diminish the effect of the adjacent negative pre- 

 cipitation, so that that system will in a manner be interrupted at the place where the positive precipi- 

 tation appears. In this way, however, the constitution of the current system will be such that the 

 characteristic areas of convergence and divergence would be prominent, and this is just what these 

 current-arrows indicate. The positive perturbing force in the vertical intensity at Gottingen also indicates 

 the existence of such a system. Without the assumption of a system such as this, it would perhaps be 

 rather difficult to find a simple explanation of these southern-pointing arrows, as the negative storms 

 seem to be fairly evenly distributed about the auroral zone. We should then have to assume a more 

 complicated constitution of the perturbing current-system, for instance, that rays came comparatively near 

 to the earth as far south as this, and that their direct effect was of the greatest importance, or some- 

 thing similar. According to what we have said above, however, assumptions such as these are not 

 necessary, our simple assumptions being apparently sufficient to explain the principal phenomena. 



On the last two charts, XI and XII, for the hours 22* //'", and 2j h /"', the strength of the 

 negative storm has considerably decreased, and we once more find traces of the positive storm, at 

 22 h 15 in Jan Mayen, and at 23'' 5 at Fort Rae. The negative storm now appears to be con- 

 centrated about the region from Ssagastyr to Cape Thordsen, i. e. on the night-side. At the south- 

 ern stations there are no great changes to be discovered. We found that the vertical arrows at 

 Gottingen must be due to the positive system; but the deflection in the curve is in striking harmony 

 with the negative storm in the north, as the deflections begin to increase simultaneously. This may 

 therefore only be indicative of the connection existing between the positive and the negative precipitation. 



