1864.] 



Disturbances at Kew and Nertschinsk. 



251 



the same distinctive features ; the local hours or maximum and minimum 

 varied at different stations, but the same two dissimilar forms were every- 

 where presented by the curves representing the two diurnal progressions. 



Having thus traced apparently two sources in which the disturbances 

 might be supposed to originate, the possible connexion of these with the 

 points of maximum attraction in the two systems of the magnetic terrestrial 

 distribution presented itself as the next object of fitting research. It was 

 inferred that if two stations were selected in nearly the same latitude, but 

 situated one decidedly on the eastern side and the other decidedly on the 

 western side of one of the points referred to, the curve of the easterly de- 

 flection at the one station would perhaps be found to correspond with the 

 curve of westerly deflection at the other station at the same hours of abso- 

 lute time, and vice versd. The Kew photograms in the five years 1858 to 

 1862 supplied the necessary data for one of the two stations, viz. the one 

 to the west of the point of maximum attraction of one of the two mag- 

 netic systems, whilst Pekin, where hourly observations from 1851 to 1855 

 inclusive are recorded in the ' Annales de I'Observatoire Central Physique 

 de Russie,' might supply a station on its eastern side. As this comparison 

 might be regarded somewhat in the light of a crucial experiment, the reliance 

 to which the Pekin observations were entitled was examined by the very deli- 

 cate test afforded by rewriting the observations recorded at solar hours in 

 hours of lunar tim.e, and examining the lunar-diurnal variation thence 

 derived. When this is found to come out systematically and well, and 

 similarly in different years, the observations which have furnished it may 

 be safely regarded as trustworthy. The Pekin observations corresponded 

 satisfactorily to this test, and in the Philosophical Transactions for 1863, 

 Art. XII., the comparison was made of the Kew and Pekin disturbance- 

 deflections, the result showing that "the conical form and single maximum 

 which characterize the curve of the easterly deflections at Kew, c^jiaracterize 

 the curve of the westerly deflections at Pekin at approximately the same 

 hours of absolute time." For a further trial of this important result, a 

 second comparison of the same kind was made, being that of the curves of 

 the disturbance- deflections at Nertschinsk from 1851 to 1857, also re- 

 corded in the * Annales de I'Observatoire,' &c., with those from 1858 to 

 1862 at Kew. Nertschinsk is about 12° north of Pekin, and is nearly in 

 the same longitude as that station, whilst its latitude is almost identical 

 with that of Kew. The Nertschinsk observations were subjected to the 

 same test in respect to accuracy as those of Pekin, and with a similarly 

 satisfactory result. The comparison of the disturbance-deflections showed 

 a still more perfect accord between the curves representing the easterly 

 deflections at Kew and the westerly at Nertschinsk at approximately the 

 same hours of absolute time. 



The present paper contains a further comparison of the nearly synchro- 

 nous disturbances at Kew and at Nertschinsk on the days of most notable 

 disturbance at both stations in 1858 and 1859, the comparison being 



