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Observations made at the Magnetic Observatory at Toronto, during a 

 remarkable Magnetic Disturbance on the 25th and 26th of Septem- 

 ber, 1841 ; with Postscripts, containing the Observations of the same 

 Disturbance made at the Magnetic Observatories of Trevandrum, 

 St. Helena, and the Cape of Good Hope. 



The interest which Mr, Airy's Circular Letter has excited on the subject of 

 the magnetical disturbance, which was observed at Greenwich on the 25th 

 of September last, makes it probable that considerable advantage may be 

 derived, by immediate publicity being given to the observations which were 

 made on the same day at the Magnetical Observatory at Toronto in Canada, 

 showing the effects of the same disturbance in America. 



In the regular course of the publication, proceeding under the direction 

 and at tlie expense of Government, of the observations made at the Magne- 

 tical Observatories conducted by officers of the Royal Artillery, several months 

 would necessarily elapse before the observations of Se^Jtember 25, 1841 , woidd 

 pass through the press. Under these circumstances, the Master-General 

 of the Ordnance has approved of their immediate publication in a separate 

 form, Avhich will enable them to be communicated at once to the Directors 

 of similar establishments in all parts of the globe ; and the Committee of the 

 British Association, appointed to conduct the co-operation of that body in 

 the system of simultaneous magnetical and meteorological observations, have 

 deemed this a fitting occasion for the emplojnnent of a portion of the grant 

 placed at their disposal. 



The abstracts received from the Observatory contain the observations ex- 

 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 aflPords 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. 



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