1864.] 



Magnetograph-traces at Kew and Lisbon, 



113 



From this Table it will be seen that the signs are always alike for the 

 different elements, and also that the small and rapid movements of the 

 horizontal force are double of those of the vertical force — a result in con- 

 formity with that already obtained by one of the writers in a previous com- 

 munication. On the other hand, the declination peaks and hollows do not 

 bear an invariable proportion to those of the horizontal and vertical force, 

 but present the appearance of a daily range, being great in the early morn- 

 ing hours, and small in those of the afternoon. Indeed this is evident by 

 a mere glance at the curves, which, it so happens, present unusual facihties 

 for a comparison of this nature. 



Comparison of Lisbon Curves. 



1. Declination- and vertical-force curves. — The peaks of the waves, or 

 the elevations in the curve of declination, are always shown in hollows or 

 depressions in the vertical-force curve, and vice versa. We have never seen 

 an instance to the contrary either in the curves under comparison or during 

 the whole time of the operation of these instruments. This curious 

 relation is exhibited in a Plate appended to this communication, from 

 which it will be seen that we have not only a reversal, but also a very 

 nearly constant ratio between the ordinates of the two curves. At Lisbon 

 therefore an increase of westerly declination corresponds to a diminution of 

 vertical force, and vice versa ; also an almost constant proportion obtains 

 between the corresponding changes of these two elements. 



2. Bifilar and Declination Curves. — July 15. A great disturbance, 

 which at 3/"' Lisbon mean time, or 9^ 13'^' 5 Greenwich mean time, 

 abruptly and suddenly augmented the horizontal force. 



The curve of the declination continues nevertheless nearly undisturbed 

 for about 30 minutes after this, and only at 9^" 4r^-5 G.M.T. it com- 

 mences to descend very slowly. 



July 16. — At about IS*" 6^" G.M.T., a very regularly shaped prominence 

 of some duration occurs in the declination, but is quite invisible in the hori- 

 zontal force. 



July 17. — We see in the bifilar curve half-a-dozen small peaks repro- 

 duced in the declination in the same direction, but to a smaller extent. 



July 18. — One or two accordant peaks. A large prominence of some 

 duration in the dechnation at about 17^" 56"^ G.M.T. is reproduced as a 

 slight depression in the horizontal force. 



July 19. — A reproduction in the declination of several small peaks of the 

 horizontal force ; nevertheless there are others also small which one does 

 not see there, or only reproduced to a small extent. Not much accordance 

 between the great and long- continued elevations and depressions. 



July 20.— An accordance between the small peaks. 



July 21.— The same. 



July 22. — The curve is well marked with small peaks. Coincidence of 

 several small peaks, but a want of agreement between the more remarkable 



