1365.] Rev. W. Sidgreaves Magnetical Observations. 67 



distances 1-0 and 1'3 foot. The value of P obtained in the preceding year 

 was 0-00217. 



The mean of the values of ^> obtained each month from deflection ob- 

 servations at the two distances 1-0 and 1*3 foot, has been adopted for de- 

 ducing the measure of horizontal force. 



Observations taken to determine the position of the zero-point on the 

 scale of the declination magnet, gave the same result as was obtained in 1859. 



The discrepancies in the Declination observations . may possibly be in a 

 considerable degree occasioned by diurnal variation, as the observations 

 varied in regard to the hour of the day ; in future this will be avoided by 

 making the observations always at a fixed hour. The discrepancies may 

 also have been in part occasioned by magnetic disturbance which we have 

 no present means of eliminating. 



OBSERVATORY. 



Greenwich O h 9 m 52 s - 68. Height above Sea-level 381 feet. 

 Magnetic Observations for 1864. 



