70 C. COLERIDGE FARR. 
feet from the place where the values of H. (the Horizontal In- | 
tensity) were taken, and thirty-four feet from that at which the 
dip was observed. Its direction is about N.W. and W.N.W. from 
these positions and the angles of depression about 24° and 19° 
4 
respectively. 
The instruments used were a Kew magnetometer No. 65, by 
Elliott Bros., anda Dip Circle by Dover, No. 78. The Kew 
certificates of these instruments are preserved at the Laboratory. 
The method used for finding H, the horizontal intensity was that 
of deflections and vibrations for which the Kew instrument is - 
constructed. 
As the corrections form an important part of the investigation, 
it may be well to mention the following points. With regard to » 
those adjustments which apply to the observation of the time of 
vibration of the needle, the first is to make sure that the axis of 
the swinging magnet is accurately horizontal. This was always 
seen to very carefully before any observation of the time of vibra- 
tion was made, and the previous day’s setting of the needle on its 
stirrup was never relied on. The temperature and induction 
coefficients was taken from the tables sent out with the instru- 
ment from Kew. The effect of the torsion of the suspending silk 
thread was determined in the usual way. The mean of six obser- 
vations gave the value of one of the scale divisions engraved on 
the magnet 1782 (Kew value 1'°77) a number which I give so 
that others using the same instrument may be saved the trouble . 
of finding it again. Two threads were used during the time the | 
observations were being taken, the first one being accidentally 
broken on November 10. The amount of deflection of the magnet 
due to turning the torsion head through 90° was with the first 
thread 3':47, and with the second 4'-47. No correction was applied 
to the observed time of vibration for clock rate as the chronometer 
gaining only °5 sec. a day, so that any error produced by taking 
the apparent second for the time second was too small to be 
appreciable. The fact that the arc of vibration was not indefi- 
nitely small was taken account of. 
