1825. j Pliilosophical T^ransac^ions for 1825, Part L 457 



A double series of observations on the diurnal changes in the 

 positions of the points of equilibrium at which a magnetic needle 

 was retained by the joint action of terrestrial magnetism and of 

 two bar magnets, having their axes horizontal and in the mag- 

 netic meridian, and their centres at the distance 21*21 inches 

 from the centre of the needle, afford by correction and calcula- 

 tion the following 



Tables of the mean Terrestrial Magnetic Intensities at different 

 Hours during the Day. 



1, From observations made within doors. 



" From the mean obtained here, it appears that the terrestrial 

 magnetic intensity was the least between 10 and 11 o'clock in 

 the morning, the time, nearly, when the sun was on the mag- 

 netic meridian ; that it increased from this time until between 

 9 and 10 o'clock in the evening; after which it decreased, and 

 continued decreasing during the morning until the time of the 

 minimum." i 



2. From observations made in the open air. ; 



