58 niRKF.I.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903. 



The following signs will also occur on the charts: 



(?) indicates that the perturbing force cannot be determined, owing to lack of material. 

 (*) See note in the text. The perturbation is then often ill-defined, and so small that the perturbing 



force cannot be calculated with any advantage. 

 (0) The perturbing force is imperceptible. 

 (0&O) Indicate respectively the sun and the moon, and these signs are placed where the sun and moon 



respectively, in the epoch under consideration, stand in the zenith. 



() Indicates the point in which the magnetic axis of the earth intersects the earth's surface, i. e. the 

 axis of the elementary magnet to which the earth approaches for infinitely great distances. At 

 the new year, 1903, this point was determined thus: North latitude 78 20', West longitude 71 n'. 

 On the Mercator's chart, the equator line for this pole-point will also often be marked. 

 () The magnetic north pole. 



To show the position of the so-called auroral zone, two curves, from FRITZ'S aurora chart, are drawn 

 on all the polar charts and on a few of the Mercator's charts. The most southerly gives the places of 

 the greatest frequency of observed aurora. The most northerly connects points where aurora is seen as 

 frequently in the south as in the north. 



It sometimes happens, in the case of the northern stations, especially Matotchkin Schar, 1902 and 

 1903, that the patch of light, owing to the strength of the perturbations and the great sensitiveness of 

 the apparatus, passes out of the paper, returning again in a little while. We know then that the deflection 

 is at least as great as to the edge of the paper. This minimum value of the perturbing force, obtained 

 by measuring to the edge of the paper, is then placed upon the chart as a dotted arrow; and at its 

 point is placed an arrow, to give the direction in which the current-arrow really has its point. 



In cases in which the total perturbing force is resolved into two partial forces, the corresponding 

 current-directions will be given with dotted arrows, while their resultant is drawn in full. 



THE COPIES OF THE MAGNETIC REGISTERINGS. 



EXPLANATION AND GENERAL REMARKS. 



24. As already mentioned, there will be a plate belonging to each perturbation, containing copies 

 of the magnetograms obtained. 



As it is important, when reading the descriptions, to have the curves themselves before one, it 

 might have been better if the latter could have been in the same place as the descriptions. The fact 

 that, notwithstanding this, we have considered it advisable to keep all the curves together, is mainly due 

 to circumstances of a purely technical nature. 



The curves will follow one another in chronological order. 



Upon the district in which the perturbation is found, the normal line will be drawn, according to 

 the previously given rules, as a dotted line. 



With a knowledge of the scale-value, it will thus be possible, if desired, to find out the perturbing 

 force at any point of time. 



The scale-value is given graphically by lines placed at the end of each curve, and giving the 

 length of oscillation of a particular force. At the head of the column are the signs L", L", and L", which 

 indicate the length of a deflection in H, D and V respectively, corresponding to magnetic force, n. y, 

 operating in the respective directions. In the middle of the line is an arrow-head, which gives the 

 direction of increasing H. I. increasing westerly declination, and increasing vertical intensity. 



The scale in relation to the original magnetograms is so arranged that all the magnetograms shall 

 have the same time-length. The scale-value is thus increased in the same proportion as the time-length 

 is diminished. 



