on the Rates of Chronometers. 



45 



Chronometer D in a Vertical Plane passing through the Centre of the 

 Iron Shell, at right Angles to the Magnetic Meridian, and to the 

 East of it. 



Distance of the I Elevation of the 

 Vertical Axis of I Centre of the 

 the Chronometer, I Face, above the 

 from Centre of | Centre of the 

 Shell. I Shell. 



10.2 Inches. 2.5 Inches 



Rate in 



Pig. 7. 



Rate in 

 Fig. a. 



Rate in 

 Fig. ». 



Rate in 

 Fig. 10, 



+ 0".5 +7".3 +e''.7 +5".l +7".l +5''.7 



Detached 

 Rate. 



The chronometer E, was, in this second set of experiments, 

 placed below the nadir of the ball, the crystal of the time-keeper 

 just touching it; and the machine was so moved, as to make the 

 positions of its balance correspond to those of the chronometer B, 

 which at the same time occupied a situation in the same vertical 

 line, or ever the zenith of the shell. The detached rate of the 

 machine E was - 2".2, and which with XII to the West, became 

 — 0".8, the same rate being- also preserved, when the last-men- 

 tioned hour was brought to the South ; but on turning the chro- 

 nometer so as to present XII to the East, the rate became - 3".2 ; 

 the decrement being considerable, in consequence of the last 

 change. This rate, however, was converted into — 2".0, by 

 allowing XII to be directed to the North ; and, by finally detach- 

 ing the time-keeper from the action of the iron mass, it farther 

 changed to — I'M. This chronometer, therefore, gained by its first 

 application to the Iron Shell, and lost when etitirely removed from 

 its influence. In two of its -positions, the rate was observed to he 

 exactly constant; in a third, the influence of the ball occasioned it to 

 lose, and in a fourth caused it to gain. 



Lastly, the chronometer F, which was not employed in the first 

 course of experiments, was now placed to the north of the ball, 

 with the extension of the magnetic meridian of the globe, passing 



