1868.] 



during the Magnetic Storm of February 1866. 



401 



we may take as the recommencement of a second period, which terminated 

 about 7 P. M. 



In the Lisbon declination we see at the beginning and end of this period 

 two similar undulations, each about half an hour in duration, and almost 

 regular. In the middle there are smaller waves, interrupted by peaks and 

 hollows. The diminution of declination is not remarkable. 



In the vertical force we have the same waves in a contrary direction to 

 the declination ; but the ascending branch is in one instance greater than 

 the corresponding descent in the declination. A similar difference may 

 be noticed in the last wave but one, by which it happens that the vertical- 

 force curve shows an increase of force during two hours and a half, without 

 a corresponding decrease of the declination. 



The horizontal force retained its position below the mean until 3^ 20'", 

 when it descended further till 4^^ ; then it ascended successively till 6^, 

 where it stopped very nearly in its normal position. 



"We will now discuss the Kew curves. The declination has been greatly 

 disturbed by large deviations above and below its normal position, a 

 general decrease of declination, however, taking place during more than 

 three hours of great disturbance. 



The needle has oscillated 40' in arc, while the Lisbon oscillations have 

 not exceeded 8'. Some movements seem to agree with Lisbon ones, 

 others, on the contrary, disagree entirely ; and even in those movements 

 which correspond, some differences of time are appreciable, which cannot 

 be due to error in the time-scale. 



The vertical force at Kew increases rapidly from 2^ 35"^ to 3^ 50"" ; a 

 period of fluctuations then follows up to b^, after which the curve rapidly 

 descends irregularly to the end. 



The Kew vertical-force curve only agrees with the Lisbon curve in the 

 general aspect of the disturbances, the period of greatest increase lasting 

 but 1^ 15^ while at Lisbon it was 2^^ 10"^. 



It should be also remarked that the vertical force does not agree in the 

 slightest with the horizontal force at Kew. 



The horizontal force at Kew seems to follow the inverse direction of 

 that of Lisbon, and its general form resembles that of Lisbon inverted. 

 After 5*" 30™ the waves appear to agree. 



Thus we see, in the same disturbance, two periods at an interval of some 

 hours, which show their relations at the two stations to be of an entirely 

 different nature. 



In the first period the three instruments agree ; in the second, the 

 horizontal components differ, and all similarity is wanting in the vertical 

 force and declination during the greater part of the total duration. 



A long calm period, 46^ in duration, followed these large disturbances ; 

 during which the series of small peaks and hollows were reproduced in the 

 three curves, chiefly in the morning (1 7^ to 21^) of the 21st and 22nd days. 



Third Disturbance.— Knoth^x disturbance commenced about 6^ on the 



