1864.] Magneto graph-traces at Kew and Lisbon. 



115 



verified by the behaviour of the Lisbon curves. From the relation, always 

 invariable, between the waves of declination and vertical force, as well as 

 from the almost total absence of agreement between these two curves and 

 the horizontal force, one has a right to conclude — 



1 . That there is approximately only one independent force which acts 

 at Lisbon, if we consider the vertical plane bearing (magnetic) east and 

 west. Now the ratio of the disturbing forces for the vertical force and 

 declination is, in units of force, between 26 : 48 and 26 : 36. This would 

 give the inclination of the resultant between 29° and 36°. 



2. The absence of agreement in time, and the variability in direction, 

 between the waves of the horizontal force and those of the declination and 

 vertical force, appear to lead to the conclusion that there is another dis- 

 turbing force besides that already mentioned, which acts in the direction of 

 the magnetic meridian and almost horizontally. 



Comparison of the Kew and Lisbon Curves (14-24 July). 



1. Horizontal force {north and south disturbing force). — The curves 

 of the horizontal force at Kew and at Lisbon exhibit a very great simili- 

 tude *, as will be seen at once from the Plate appended to this communi- 

 cation. Almost all the waves and peaks and hollows are reproduced at both 

 places. At the same time one does not see the same resemblance during 

 the great disturbance of loth July. In the commencement, and for the 

 first four hours, there is a resemblance for all the waves, but from that 

 time until IQi^'G.M.T. one remarks little agreement between the different 

 elevations and depressions. But from 19^^ until the end of the dis- 

 turbance the likeness reappears. There are, however, one or two cases of 

 small resemblance in the other curves, but these are of short duration. 



In order to demonstrate the similarity between the two curves, reference 

 is made to Table II., in which the principal points are compared together 

 with respect to time ; that employed being the mean time for both 

 stations. 



From this Table it will be found that the average difference between the 

 local times of corresponding points is 34"^'3, while that due to difference of 

 longitude is So'^'S. We attribute this apparent want of simultaneity to 

 various causes : — • 



(1) Loss of time in the commencement of movements of the registering 

 cylinder. 



(2) Difficulty in estimating precisely the commencement of certain curves. 



(3) It was only in the month of xlugust that the exact Lisbon time of 

 the astronomical observatory was obtained by a telegraphic connexion. 



(4) To these must be added the uncertainty in estimating the exact 

 turning-point of an elevation or depression of a blunt or rounded form. 



* We speak of the Kew cm-ves reversed so as to hare their base4ines above, the dis- 

 position of the registering arrangement at Kew being the opposite of that at Lisbon. 

 This reversal has been made in the Plate which accompanies this paper. 

 VOL. XTIT. K 



