RECORDS OF DISTURBANCES AT CO-OPERATING STATIONS. 153 



CHAPTER VIII. 

 RECORDS OF DISTURBANCES FROM CO-OPERATING STATIONS AND THE ANTARCTIC. 



55. What I had scon of the quick-run curves, obtained at Kew on the international term days of 1902 

 and 1903, made me anticipate that, so far as the inter-comparison of disturbances at different stations was 

 concerned, the term-hour data were likely to prove of little service. Examination of the results obtained 

 elsewhere, so far as available, and of the Antarctic records only served to confirm this. Accordingly I 

 came to the conclusion that if any comparison of disturbances was to be carried out, additional data must 

 be obtained. With this object, a list was made of days during 1902 and 1903 on which it appeared 

 probable, from a consideration of the Kew and Atitarctic curves, that comparative data from different 

 stations would be valuable, and in January, 1905, a circular was issued, in the name of the Royal Society's 

 Magnetic Committee, requesting that copies of the magnetic curves obtained on the days in question 

 should be transmitted. This was sent to Dr. C. C. FARR, Director of Christchurch Observatory, New 

 Zealand ; Mr. C. T. F. CLAXTON, Director of the Royal Alfred Observatory, Mauritius ; and to 

 Mr. N. A. F. Moos, Director of the Colaba Observatory, Bombay. These gentlemen all gave favourable 

 consideration to the request, and sent home a number of most valuable records. The copies received 

 from Christchurch and Colaba were photographic, those from Mauritius were tracings of the original. 

 After considering all the material, I made a selection of the disturbances which presented most points of 

 interest, and these are dealt with here. Even in 1902 the Kew curves, especially those of Vertical 

 Force, were sensibly influenced by electric-traction currents, and accordingly application was made to 

 Mr. E. KITTO, Superintendent of Falmouth Observatory, for the loan of the Falmouth magnetic curves 

 for the days selected. Mr. KITTO and the Committee of the Falmouth Observatory responded favourably 

 to this request so far as was possible. The Falmouth Vertical-Force magnet was unfortunately out of 

 action during part of 1902, so that the information for that element during this time was derived from 

 Kew alone. So far as the disturbances here considered are concerned, the differences between the Kew 

 and Falmouth curves are mostly infinitesimal. In general, I measured both sets of curves. In the 

 discussion I chiefly use the Kew measurements, but the plates show the Falmouth curves. It will be 

 most convenient to describe first the plates dealing with curves from Falmouth, Colaba, Mauritius, 

 and Christchurch, and then the plates dealing with the corresponding Antarctic curves and some 

 additional ones. 



FALMOUTH, COLABA, MAURITIUS, AND CHRISTCHURCH DISTURBED CURVES. 



56. The magnetographs in use at Falmouth, Colaba, Mauritius, and Christchurch are of what is 

 known as the " Kew " pattern. The time scale of the present Kew magnetograph is 1 hour to 0'6 inch 

 (15 '25, cm.), and this, presumably, was what was aimed at in the case of the magnetographs at the four 

 stations mentioned above. As a matter of fact, the time scales, though very nearly equal, are not 

 absolutely so. Still, the difference is so small that it does not readily catch the eye when the curves are 

 juxtaposed, unless one extends the comparison to a large number of hours. This enables an effective 

 comparison to be readily made without modifying the scale values. 



The curves in Plates XIV to XXI were actually derived from copies of the curves received from 

 Falmouth, Colaba, Mauritius, and Christchurch, which were made with the Schmidt curve tracer. The 

 tracing was done at Bushy House by Mr. BROOKES, under the supervision of Mr. F. J. SELBY. The 

 scales, whether of ordinates or of abscissae, can be altered with the Schmidt tracer at the will of the operator, 

 but, as a matter of fact, no intentional departure was made from the scales in the original curves. The 

 tracings were made on separate sheets of paper, which were then arranged one below the other. In the 

 originals the time is shown by breaks occurring every 2 hours in the time line, either at the even or at 

 the odd local hours. The original time lines were dispensed with and replaced by others in which hours 

 G.M.T. are indicated by short transverse lines. These lines were put on with considerable care, but they 

 cannot claim to be more than approximately correct. 



X 



