on the Rates of Chronometers. 37 



many horizontal sections are given, for the purpose of illustrating 

 the alterations produced in the positions of the balances and main 

 springs, in consequence of the time-keepers having been turned 

 round their vertical axes during the successive experiments, to 

 discover the changes of rate resulting from the different positions 

 of those parts of the machine, v/ith respect to the ball and the 

 magnetic meridian. The constant distances of the vertical axes of 

 the chronometers from the centre of the sphere, together with the 

 elevations or depressions of the centres of their faces, above the 

 same point, are entered in the respective tables. The time-keepers 

 employed were those of the box kind. 



The first experiment was with the chronometer A, placed to the 

 north of the shell, having the centre of its balance in the magnetic 

 meridian of the iron mass, and the hour of XII directed to the 

 north. The position of the time-keeper was also so regulated, 

 that the centre of its face might be in the plane of the magnetic 

 equator of the ball. The result of this application was, an increase 

 of the rate of the chronometer from -f 9".7 to + 10".7, the rate in 

 this and all the subsequent experiments, being determined by the 

 mean of four days' observation. By turning the time-keeper a 

 quadrant, so as to make it occupy the position denoted hy A, 

 Fig. 2, with XII pointing to the east, and the centre of the balance, 

 in a situation at right angles to its former position, the rate was 

 augmented to + 11".3 ; and, by again turning it a quadrant, so as 

 to bring the balance again into the magnetic meridian of the ball, 

 as in Fig. 3, the daily variation became + 12".6; and by again 

 moving it through another similar space, into the position denoted 

 by A, Fig. 4, the rate declined to + II" A. When detached from the 

 iron mass, the rate was found to be + 12".8, the time-keeper 

 having increased its rate + 3".l, in consequence of its application 

 to the shell. Hence the influence of the ball occasioned an 

 unequal increase of rate in the chronometer in all its -positions ; the 

 mean of the four being + 1 1".6, which is an increment to its detached 

 rate of 1".7. Jt will also he perceived, that the greatest increment 

 the time-keeper received, was produced when the balance was farthest 

 removed from the attracting mass ; and the least alteration of rate, 

 when nearest to it ,• and that the positians (2, 4) at right angles to 



