90 Eev. S. J. Perry on a Simultaneous Disturbance [May 18^ 



"Note on a Simultaneous Disturbance of the Barometer and 

 of the Magnetic Needle.'' By the Eev. S. J. Perry, F.R.S. 

 Beceived April 27, 1876. 



As any question of the connexion between the di:fferent phenomena of 

 nature may be of interest, I will venture to call attention to an observa- 

 tion made, in February last, in China, which tends to estabhsh a fresh link 

 between terrestrial magnetism and meteorology. 



Prom the curves that accompany this note (p. 91), it would seem that the 

 same cause may be capable of producing a simultaneous perturbation of 

 the barometer and of the suspended magnets. 



At the newly established observatory of Zi-Ka-"Wei, near Shanghai, 

 no very considerable disturbances of the magnetic elements have been ob- 

 served in 1874 and 1875 ; but on Pebruary 20, 1876, the director, the Eev. 

 M. Dechevrens, had the good fortune to notice the first irregularities 

 of any great extent that had ever been observed in China ; and these 

 movements were found afterwards to be almost identical in all their in- 

 flexions with those traced by the mercury in the barometric curve. The 

 first observations on the morning of the 20th showed an increase of 

 westerly declination and of dip, with a diminution of the horizontal com- 

 ponent of the intensity, the observed value of H.P. being the least ever 

 recorded at this station. Prom 10*" 32"^ a.m. Mr. Dechevrens was able 

 to give his whole attention to the declination-magnet, which was then 

 moving westward with a risiug barometer. The barometer attained a 

 maximum about 10^ 48°^ a.m., followed by two westerly maxima of 

 declination at 11 a.m. and 11.40. Prom 10^' 48°^ until shortly after 4 

 P.M. the barometer fell rapidly, the magnet in the mean time moving 

 almost constantly in an easterly direction, attaining its least declination 

 of 1° 55' -07 W. at 4^ 24^^' p.m. The amplitude of the declination dis- 

 turbance was 10''33, a large amount if we consider that the mean diur- 

 nal range scarcely exceeds 3'-5 in the winter months. On the previous 

 evening the passing clouds appeared to be lib up on their borders, possibly 

 by an aurora. A N.E. wind blew very constantly throughout the day, 

 and the rain fell from 3 p.m. until the following morning. 



The dotted line represents the range of the declination-magnet on 

 Pebruary 21. 



S. J. Peeet. 



Stonyhurst Observatory, 

 April 26, 1876. 



