1868.] 



Comparison of Magnetic Curves, 



399 



May 28, 1868. 



Lieut.- General SABINE, President, in the Chair. 



The following communications were read : — 



I. "^^A Comparison of the Kew and Lisbon Magnetic Curves 

 during the Magnetic Storm of February 20-25, 1866/' By 

 Senhor 1. Brito Capello, of the Lisbon Observatory. Com- 

 municated by B. Stewart. Received April 18, 1868. 



During the 20th, 21st, 23rd, 24th, and 25th of February 1866, large 

 magnetic disturbances were recorded by the magnetographs at the Lisbon 

 and Kew Observatories. 



As these indicate several appreciable deviations from the normal types, 

 I trust a description of them may be not without interest to the Royal 

 Society. Dr. Stewart, Director of the Kew Observatory, has kindly sent 

 me copies of the Kew magnetic curves during these disturbances. 



In order thoroughly to ascertain the laws governing the forces which 

 disturb the ordinary magnetic condition of the globe, we should reduce 

 in a systematic manner, such as General Sabine has so ably pursued, the 

 observations made at a number of stations, and then classify and discuss 

 the valuable results so obtained. 



Nevertheless the present communication relative to the disturbances ob- 

 served at two stations offers some interest, on account of the apparent 

 variabihty of the forces which are in action during the same disturbance, 

 and also the apparently variable relations between these forces at Lisbon 

 and the same forces at Kew. 



In a former comparison made between the magnetic curves of Kew and 

 Lisbon (Proceedings of the Royal Society, No. 60), it was established 

 that at Lisbon, during disturbances, the vertical force and the declination 

 curves were invariably opposed to each other, i. e. a concave wave of one 

 of the curves always corresponded with a similar convex one in the other ; 

 or, in other words, an augmentation of the vertical force agreed with an 

 horizontal movement of the north pole of the bar towards the east, and a 

 diminution of the same component to a movement of the north pole to 

 the west. 



This general law applied both to the large and slow movements (waves), 

 and the short and rapid ones (peaks and hollows). 



However, there were some very rare instances in which this law did not 

 altogether hold good. In these cases, although the peaks and waves were 

 reproduced in the two curves in inverted order, yet the whole of the one 

 curve for some period did not assume the inverted form of the other 

 curve. 



The periods of disturbance which are the objects of this discussion 

 belong to these abnormal types. 



