Magnetic Disturbance on September 25t?i and 2Qth, 1841. 147 



pressed in the scale-divisions in which they are read : these have been con- 

 verted by Lieut. Riddell, R.A., both in the tables and plate, into the more 

 convenient forms, — of angular value for the declination, — and for the horizontal 

 and vertical force, of the proportion which the changes of those forces bear 

 to their whole amount. The plate also shows the mean daily curve of each 

 element during the month of September, the comparison of which with the 

 curve on the 25th affords a measure of the magnetic disturbance on that day, 

 both being reduced to the same Zeros. 



The perseverance with which the magnetometers were followed during 

 twenty hours, by observations taken at intervals of a minute and a half, is 

 highly creditable to Lieut. Younghusband and his detachment. 



Edward Sabine, Lieut.-Col. R.A. 



Woolwich, Dec. 10, 1841. 



OBSERVATORY AT TORONTO, CANADA. 



Abstract of Observations taken during a remarkable disturbance on the 

 25th and 26th September, 1841. 



L2 



