43 



Mr. Harvey on the Effects of Magnetism 



situation at right angles to the meridian of the ball, the rate 

 declined to + 10".9, and which rate it nearly preserved, in the 

 position of A, Fig. 9, the rate in this situation being + 10".8 ; but, 

 on turning it into the position of A, Fig. 10, the daily variation 

 augmented to + 12".2 ; and, on finally detaching the chronometer, 

 the rate was found to be + 9".9, agreeing within 0".2 of its 

 detached rate, prior to the first experiment. 



Three remarkable circumstances were disclosed by this experi- 

 ment In the first place, a considerable declension in the rate took 

 place, by removing the chronometer from the position in which its 

 balance was nearest to the attracting mass, as A, Fig. 7, into the 

 situation denoted by A, Fig. 8, where the line joining the centres 

 of the balance and chronometer, was at right angles to the meri- 

 dian of the balance ; and secondly, an acceleration equally sudden 

 was produced, by removing the time-keeper from the position in 

 which the balance was farthest from the iron ball, as A, Fig. 9, into 

 the position of A, Fig. 10, where the line connecting the centres of 

 the time-keeper and balance, was again at right angles to the 

 meridian ; and thirdly, that the acceleration communicated to the 

 detached rate, in consequence of the first application of the time- 

 keeper to the action of the ferruginous, was entirely removed by 

 the cflPect produced during the second set of experiments. 



Chronometer A in the Magnetic Meridian of the Iron Shell, and to the 

 South of it; 



Distiince of Ihi 

 Vertical Axis o 

 he Chronoiuettr, 



Depression of lli( 



Centre of the 



F-.ice, below the 



Centre of the 



Shell. 



Detached 

 Rite. 



Rate in 



Fig. 7. 



Kate in 



Tig. 8. 



Rale ID Rate in 

 Fig. 9. Fig. 10. 



Detached 

 Rate. 



8,9 Inches. 



2.5 Inches. +12".8 +12".4 +10".9 +10".8 +12".2 + 9".9 



In the next place, the chronometer B, which in the first set of 

 experiments, occupied a situation to the south of the ball, was 

 now placed immediately above its zenith, as in B, Fig. 7, 11, or 12, 

 with XII pointing to the West ; and which occasioned its rate to 

 alter from — 7".l to— 6".6 ; but, on turning it a quadrant, so as to 

 bring XII to the South, tlie daily variation became — 7".0, and 

 which was altered to — 7".2, when XII was directed to the East. 



