38 BeppickeEr—On the Influence of Magnetism on the Rate of a Chronometer. 
Hence follow the mean rates :— 
Figure XII directed dowards North — 4°64 
” ” ” ” East — 8-70 
” ” ” ” South = 9-6ill 
West — 5°71. 
9) ) 9 9) 
We have therefore for the daily rate G with fig. XII in any azimuth 4, 
G = — 7°16 + 2°48 cos A — 1°50 sin A, 
where 7°16 is the general mean, 2°48 half the difference of the north and 
south, and 1°50 half the difference of the east and west rates. It is further 
1°50 
tang 31 = 48 
This formula shows that the smallest losing rate is— 4°26, and takes place when the 
figure XII is directed N. 31° W. The largest losing rate is — 10°06 when the 
figure XII lies in the direction 8.31° E. The largest difference of rate, dependent 
upon the chronometer’s position is therefore 5°80. 
Airy then proceeds to describe his way of compensating the influence of terres- 
trial magnetism, and gives his observations made in order to test its effect. We 
shall reproduce this part of his Paper later on, when dealing with all the 
different methods proposed for the same purpose (ef. p. 46). 
The above formula is very interesting, since by it the points of maximum and 
minimum effect are to be ascertained. We see, for instance, that these two points 
lie in opposite directions. But assuming, as is generally the case, the balance to 
lie in the line XII—VI (cf. Harvey’s figures on Plate I.), we remark, that the. 
extreme effects do not take place with the balance in the magnetic meridian ; 
we only perceive that the largest losing rate is reached when the balance 
is nearer to the north than it is when the smallest losing rate is observed. 
The reason of these peculiarities lies, most likely, in the special distribution of 
fixed magnetism in the balance, or, as the following observations of Airy make 
probable, in the spiral spring. Any detailed information as to this magnetic 
quality is, however, not to be derived from the observations. It would be very 
valuable to apply the formula to other chronometers and not only to experi- 
ments like Airy’s, but to magnetic experiments also. This is, however, hardly to 
be done with the observations we have discussed till now, since on account of the 
excentricity of the balance the values are not quite comparable, if the distance of 
the influencing magnet is reckoned from the centre of the chronometer’s box. It 
would further be of great interest to see, whether the observed rates follow 
throughout the same law as in Airy’s instance or not. At first sight—if we 
especially compare Harvey’s results on p. 26—this does not appear to be the 
case. 
nearly, and 5°80 = 2,/2:48" + 1:50*. 
