BIKKKI.AND. TIIK XURWKC.IAX AURukA I'OI.AKIS KXI'KIMTIOX, !9O2 



THE PERTURBATIONS OF THE 1st NOVEMBER, 1882. 



ll'l. XXIlIi. 



}{o. 1 he striking resemblance that these perturbations bear to the two preceding storms, is appa- 

 rent on a first glance at the copies of the curves. All the storms occur at the same time of <lav; they 

 are on the whole very characteristic and well-defined; the direction of their deflections is the same ; they 

 are <>f mure or less the same strength; anil they are preceded by a Comparatively <|uiet period. 



In this case, too, it will be best to divide the period into two sections, the first being from io''to 

 about 16'' 30'", the secund from about 1 6 1 ' 30'" to 23'' ao" 1 . 



This division, however, dues not, as in the case of the preceding perturbations, suit all stations 

 equallv well. The conditions at Jan Mayen and Godthaab in particular, do not admit of a natural divi- 

 simi such as this. 



The principal phenomenon in the first section is the powerful negative storm that we find in North 

 America. 



This storm is exceedingly characteristic and well-delined, anil the perturbing forces, during the 

 time when the storm is at its height, are ol very considerable strength. Thus at I'glaamie, the oscilla- 

 tions are so great that the needle for the horizontal intensity between 14'' and 15'' is deflected beyond 

 the field of observation, and onlv re-enters it now and then, namely, at 14'' 5'", 14'' io nl and J4 h 2o m , 

 so that there are once more definite readings for these hours. The strongest perturbing forces, it will 

 be seen, appear at Uglaamie, and we must therefore look tor the storm-centre of this negative system 

 of precipitation in the neighbourhood of that station. 



The/ storm-centre on this occasion is a little more easterly in position than in the storms in the 

 first section of' the two preceding perturbations. At the same, the conditions at Ssagastyr are also some- 

 what different. \Ve there have now distinct effects of the negative system of precipitation. The forces 

 are not so strong as at Uglaamie, but the curve has a very jagged character. At first the perturbing forces 

 in the declination are directed eastwards, and in magnitude considerably exceed those in the horizontal 

 intensity. Subsequently, at 14'' 15"', the deflections are reversed, and after 14'' 20'" there are only small 

 values of l' r/ , which is now east, now west; and from that hour the perturbing forces in the horizontal 

 intensity are the predominating. This station is thus evidently situated to the west of the centre of the 

 negative storm, although probably actually in the field of precipitation. In the first section of the two 

 preceding storms, we did not find at Ssagastyr any special effect of the negative system of precipitation, 

 which was also found during these two storms in North America. 



\\V found, on the contrary, more or less distinct effects of a positive system of precipitation. At 

 Uglaamie, on the other hand, the conditions during these two preceding storms were exactly analogous 

 to the conditions we now find at Ssagastyr. In these regions, during the first section of the perturba- 

 tions, there appears a negative system, which, in its behaviour and character, exactly corresponds with 

 those- we found during the two preceding storms; but the position of the system on this occasion has 

 moved a little westwards, so that the conditions at Uglaamie during the preceding storms, answer to 

 those at Ssagastvr during the present storm. 



It will be well to carry the comparison still further, and see how far the conditions at the other 

 stations are analogous to those we have formerly found. Before doing so, however, we will remind the 

 reader of what we said in the two [in-ceding perturbations regarding the conditions at C'ape Thordsen 

 during the first section. It appeared from the curves that simultaneously with the powerful negative 

 storm in North America, a negative storm also occurred at Cape Thordsen, counteracting the positive 

 storm which prevailed during the period before; and after, and causing the deflections to some extent to 

 alter, so that we found negative values of />, at the hours at which the storm in America had its maxi- 

 mum. During the present perturbation, in the interval before the powerful negative storms, there is no 



