MAGNETIC DECLINATION AT KEW AND NERTSCHINSK. 
239 
and the comparison of the disturbance-deflections showed a still more perfect accord 
between the curve representing the easterly deflections at Kew and the westerly at 
Nertschinsk at approximately the same absolute hours. 
To this it should be added that at each of these stations, as at all others, the forms of 
the easterly and westerly deflection-curves are so distinct that they cannot be mistaken 
for one another : the difference is well shown in figs. 1 and 2 of plate 1 in the “ Reade 
Lecture delivered in the Senate House of the University of Cambridge in May 1862 : ” 
the curves there represented are those of the east and of the west deflections at Kew and 
at Hobarton (in Tasmania); and on the same page the westerly curve at Nertschinsk, 
shown in fig. 3, is seen to accord with the easterly curve at Kew, fig. 1. In Plate XIII. 
accompanying the discussion of the Kew observations (Phil. Trans. 1863, Art. XII.), the 
easterly curve at Kew and the westerly at Nertschinsk are also shown in figs. 1 and 5; 
these figures represent the ratios derived from the aggregate values of the respective 
disturbance-deflections at Kew from 1858 to 1862, five years, and at Nertschinsk from 
1851 to 1857, seven years. My purpose on the present occasion is to show the corre- 
spondence between these deflections (the easterly at Kew and the westerly at Nerts- 
chinsk) in what may appear to some a more impressive manner, viz. a direct comparison 
of nearly synchronous disturbances in absolute time in the easterly and westerly disturb- 
ances at the two stations, Kew and Nertschinsk, on the most notable occasions of dis- 
turbance in the years 1858 and 1859. I am limited to these two years because the 
photographic record at Kew did not commence until January 1858, whilst the hourly 
observations at Nertschinsk for 1860 and the succeeding years have not yet reached 
England. 
I have adopted the same characteristic at both stations for the days of most notable 
disturbance, viz. all those days in which twelve at least of the twenty-four equidistant 
epochs were disturbed to an amount equalling or exceeding “ the separating value,” viz. 
3'-3 at Kew, and 3'-5 at Nertschinsk; the differences from the normals of the same 
month and hour at Nertschinsk being entered in the Table at the close of this paper, 
as those at Kew were in the Table in the Philosophical Transactions for 1863, Art. XII., 
p. 27 4, with which it may be compared. The number of days so characterized in 1858 and 
1859 are at Kew forty-two, and at Nertschinsk forty-four ; a great part of the disturbances 
being on the same days at both stations, but not invariably so, since, as is known, 
“ a disturbance affecting one element at one station does not always affect the same 
element at another station.” In inspecting the Summary at the close of the Table, it 
must be borne in mind, on the one hand, that a very regular progression can scarcely be 
looked for from disturbances occurring in the very limited space of two years ; but, on 
the other hand, that 1858 and 1859 were years of maximum disturbance in the decen- 
nial period, and are therefore years of peculiar suitability in the case of a very limited 
comparison. The aggregate value of the disturbances at Nertschinsk in 1854 was 3497 
minutes of arc, and in 1859 5602 minutes*. 
* An inquiry into the years corresponding to the epochs of minimum of the decennial variation from 1823- 
