chronometers by the proximity of masses of iron. 369 
fidence which is due to the dailv rates of the chronometers 
on those days on which the sun's transit could not be taken. 
The fourth column gives the quantity which each chro- 
nometer was fast or slow of mean time every day at noon, 
and from which is drawn the daily rate indicated in the fifth 
column. 
The sixth column shows the mean daily rate for each 
period while the chronometers remained in the same position ; 
and in the seventh , is shown the gain or loss in each position ; 
it is found by taking the difference between the actual ob- 
served daily rate, and the mean detached rate. By the mean 
detached rate , is to be understood the mean rate on all those 
days when the chronometers were not applied to the ball. 
In order to ascertain whether any law subsisted between 
the gain or loss of the watch and the magnetic intensity 
of the place in which it was situated, the needle, described in 
a preceding page, was vibrated in every situation where a 
chronometer had stood, and the mean time of its making ten 
vibrations carefully noted and entered in the eighth column ; 
and in the ninth is given the proportional magnetic intensity, 
assuming that due to the natural state of the needle at 100. 
In the tenth and last column, is described the particular 
situation of each chronometer, viz. its azimuth, height from 
the floor, and distance from the centre of the ball. These 
situations are also reduced to their particular latitudes, longi- 
tudes, and central distances, as referred to the ideal sphere 
circumscribing the ball, and explained in a preceding page. 
I have also, in every case, noted the direction of the chro- 
nometer itself, by stating whether the 12 o'clock mark on 
the dial pointed to the north, south, east, or west. 
