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



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

 local times of corresponding points is 33"^' 1 , while for the horizontal force 

 this was 34°^*3, and for the declination 34'^'0, the mean of the three being 

 33"^- 8. The measurements from which these numbers were obtained were 

 made at Lisbon independently for each element : another set of measure- 

 ments, made at Kew, but of a less comprehensive description, gave a mean 

 difference in local time of 33"^* 7, which is as nearly as possible identical 

 with the Lisbon determination. We have already observed that we attri- 

 bute the difference between 33"^" 8 and 35™ '3, the true longitude-difference 

 of local times, to instrumental errors, and not to want of simultaneity in the 

 corresponding points. 



In Table VII. we have a comparison in magnitude and sign of the peaks 

 and hollows at the two stations. 



From this Table it will be seen that the magnitude of these is generally 

 greater at Kew than at Lisbon. The curious fact of the reversal in direc- 

 tion of the vertical-force peaks between Kew and Lisbon has been already 

 noticed. 



"We shall now in a few words recapitulate the results which we have 

 obtained. 



1. In comparing the Kew curves together for this disturbance, the 

 peaks and hollows of the horizontal force always bear a definite proportion 

 to those of the vertical force, the proportion being the same as that ob- 

 served in previous disturbances. On the other hand, the declination peaks 

 and hollows do not bear an invariable proportion to those of the other two 

 elements, but present the appearance of a daily range, being great in the 

 early morning hours, and small in those of the afternoon. The peaks and 

 hollows are in the same direction for all the elements. 



2. In comparing the Lisbon curves together, the elevations of the decli- 

 nation-curve always appear as hollows in the vertical-force curve, and vice 

 versd, and there is always a very nearly constant ratio between the ordi- 

 nates of the two curves. The horizontal- force curve, on the other hand, 

 presents no striking likeness to the other two. We conclude from this 

 that there are at least two independent disturbing forces which jointly in- 

 fluence the needle at Lisbon, but that the declination and vertical-force 

 elements are chiefly influenced by one force. 



The peaks and hollows are generally simultaneous for the three curves. 

 The direction of these is the same for the horizontal force and declina- 

 tion, while that for the vertical force is opposite. The ratio in magnitude 

 of the peaks and hollows is generally variable between the horizontal force 

 and the declination, while it is always constant between the latter and the 

 vertical force. 



3. When the Kew and Lisbon curves are compared together, there is a 

 very striking likeness between the horizontal-force curves, one perhaps 

 somewhat less striking between the declination curves, and very little like- 

 ness between the vertical-force curves. It is perhaps worthy of note that 



