156 



RECORDS OF DISTURBANCES 



The disturbance on November 6 had also a sudden commencement at about 3.52 p.m., G.M.T., but in 

 this case the commencing movement was of a distinctly double character, this being very clearly shown by 

 the Falmouth curve which is reproduced. The first movement in H was a decrease, lasting for about 

 H minutes, and it was followed by a notably larger increase. The upward movement will be seen to 

 hesitate, and then diminish in steepness. The summit at Falmouth was reached about 3.58 p.m. The 

 amplitude of the first change was about ly, that of the second about 9y, but exact measurement of the 

 first movement was difficult. The Falmouth D trace shows a corresponding oscillation, a movement of 

 about 0' 5 W. being followed by a larger but slower movement of about 0' 9 E. There was no Fulmouth 

 V curve; no measurable change appeared in that at Kew. The H and D curves at Kew appeared 

 identical with those at Falmouth. 



On November 24, as appears from the lowest curve in Plate XV, there was a disturbance of considerable 

 magnitude at Christchurch. It did not, however, have a very definite commencement, and identification 

 of corresponding movements at Christchurch and Falmouth could not be satisfactorily carried out. 



59. Plate XVI shows what appears to have been the most outstanding commencement exhibited by any 

 of the magnetic storms experienced during 1902-3. The top and bottom curves are Declination ones, 

 the others are of Horizontal Force. In the latter element, the initial movement was an increase at all the 

 stations whose curves were reproduced. The copy of the Falmouth curve in Plate XVI suggests the 

 presence of a small tremor before the upward movement commenced, but this tremor is very doubtfully 

 shown in the original, either at Falmouth or at Kew. Neglecting it, the initial movement commenced at 

 11.25, and lasted until 11.29 p.m. on April 5. In the case of the Declination, the commencing movement 

 at Kew and Falmouth was unquestionably double. For the first half minute or so, there was a small 

 easterly movement, and then a much larger westerly movement, culminating at 11.29 p.m. Comparing 

 the conditions at 11.25 and 11.29 p.m., we have for the changes in the three elements the following 

 approximate values : 



Only Horizontal-Force curves were available for Mauritius. 



Of the gaps apparent in the curves most are due to interruption of the trace by the time-shutter. The 

 longer one at Mauritius represents the changing of the photographic paper. 



The disturbance was most active between 2.30 and 5.30 a.m. on April 6th, but it was by no means 

 large at any time, the Declination range at Kew and Falmouth being only about 25'. 



60. Plate XVII shows some curves whose chief interest lies in connection with some Antarctic curves, 

 which will be discussed presently. 



The very symmetrical-looking movements shown by the D, H, and V traces at Christchurch, on June 19, 

 1903, occurred during a day which was otherwise very quiet. 



The Christchurch curves of July 26, 1903, show what was for that station a very considerable 

 disturbance. They illustrate what seems a general feature the relatively small range of Vertical-Force 

 disturbances at Christchurch, compared to those in the other elements. 



The same phenomenon is also exhibited by the curves of Plate XVIII, which show the disturbances at 

 Christchurch on August 22, 1903. This was one of the largest disturbances exhibited by the curves 

 received from Christchurch. The storm showed no very definite beginning or end. The most 

 distinctive movements are those occurring about 5 a.m. and 9 a.m. But even in their case the turning- 

 points for the different elements do not synchronise satisfactorily, and no satisfactory comparison proved 

 possible with the curves at other stations. 



