114 Senhor Capello and Mr. B. Stewart — Comparison of [Jan. 28, 



peaks. The peaks of the horizontal force more developed than those of the 

 declination. 



July 23. — The same appearance of the horizontal- force curves. One 

 remarks on 22nd and 23rd that the small peaks of the declination and 

 horizontal-force are more numerous and more developed in the morning 

 hours. 



July 24. — Agreement between the small peaks. A strong disturbance 

 about lOJ^ G.M.T., no agreement between the waves. A well-marked pro- 

 minence of declination (1 5 J^) does not alter at all the horizontal-force curve. 



"We derive the following conclusions from the comparison which we 

 have made between the Lisbon curves : — 



1. The waves and the peaks and hollows of declination are always repro- 

 duced at the same instant in the vertical force, but in an opposite direction ; 

 that is to say, that when the north pole of the declination-needle goes to 

 the east, the same pole of the vertical-force magnet is invariably plunged 

 below the horizon, and vice versa. During five months of operation of 

 these instruments there has not been an example of the contrary. 



2. The more prominent disturbances of the horizontal force do not in 

 general agree with those of the declination or vertical force either in dura- 

 tion or time. 



It is certain that when one of the two elements (bifilar or declination) is 

 disturbed, the other is also ; and sometimes one appears to see even for 

 several periods of one of the curves, an imitation of the general march of 

 the other ; but when this is examined a little more minutely, and rigorous 

 measures are attempted, one easily perceives that the phases do not arrive 

 at the same time, but sometimes later and sometimes earlier, without any 

 fixed rule. 



In the same curve one generally sees contradictions of this kind. 

 Nevertheless it is certain that the agreement in direction and time is more 

 complete when the elevations or depressions are of shorter duration. 



3. The small peaks and hollows are generally simultaneous for the 

 three curves. The direction of these is the same for the horizontal force 

 and declination, while that for the vertical force is opposite. 



The ratio in size of the peaks and hollows is generally variable between 

 the horizontal force and the declination, while it is always constant be- 

 tween the latter and the vertical force. 



Our next deduction requires a preliminary remark. It has been shown 

 by General Sabine, that if the disturbances of declination at various places 

 be each divided into two categories, easterly and westerly, these obey dif- 

 ferent laws of daily variation, this difference not being the same for all 

 stations. 



This would seem to indicate that for every station there are at least two 

 simultaneous disturbing forces acting independently, and superposed upon 

 one another. 



This interesting conclusion, derived by General Sabine, appears to be 



