ON COMPARING AND REDDCING MAGNETIC OBSERVATIONS. /O 



V. Note by the Bev. Professor Perry and Professor Stewart. Coi7iparison 

 of Magnetograms of Kew and StonyJmrst. 



The existence of two magnetic observatories not veiy far apart, and 

 supplied with similar sets of self-recording instruments, affords a very 

 favourable opportunity for discussing the lesser variations that may be 

 detected in the simultaneous movements of the magnetic needle. A first 

 comparison was therefore made in 18G8 between the declination magneto- 

 grams of Kew and Stonyhurst, and it was found that the ratio between 

 the changes at the two stations was a variable one. A further discussion 

 of the curves of 1883 and 1884 has lately been made by the Rev. S.J. 

 Perry and Dr. Balfour Stewart, and the results communicated to the 

 Royal Society in a paper read on December 10, 1885, The observed 

 difi"ei'ences in the declination ordinates between the turning-points of 

 certain marked fluctuations in the curves have led to the conclusion that 

 the fluctuations at both observatories follow the same general law as to 

 direction, but that there is apparently a slight diff'erence of duration at 

 the two stations in the case of some short period movements. In dis- 

 cussing the tabulated measurements it was assumed as a M'orking hypo- 

 thesis that the disturbances are due partly to true magnetic cJianges 

 and partly to secondary currents arising therefrom. The ratios of the 

 simultaneous changes at Kew and Stonyhurst show that the angular values 

 of the declination disturbances are in excess at the latter observatory, 

 especially when the movement is of short duration ; but these ratios 

 appear to be independent of the extent of the oscillation. 



The Rev. S. J. Perry and Dr. Stewart are continuing this research. 



VI. Note by Professor Stewart and W. L. Carpenter, Esq. 



We have reduced other four years of Kew declination disturbances aftei' 

 the method described in the last report of this Committee, and have 

 obtained the following result from the two series of four years each : — 



Supposed connection between disturbances and the Moon's age. 



(0) = new (4) = full moon. 



(0) (1) (2) (3) (4) (5) (fi) (7) 



1866-69 . 88 91 78 64 52 69 74 75 



1870-73 . Ill 114 104 95 83 94 107 101 



From this it will be seen that the results obtained from both series 

 agree together in exhibiting the same sort of fluctuation. 



We have likewise reduced the four years of Kew declination disturb- 

 ance, 1870-73, with the view of determining whether there is any 

 apparent connection between wind values and magnetic disturbances. In 

 doing this we have adopted the following procedure : — 



1. We have obtained, by the kindness of the Kew Committee, the 

 total amount in miles gone over by the wind at Kew for each 

 day of the years 1870-73, and have then converted these into 

 daily averages of three days. Let us call this table A. 



