DETERMINATION OF MAGNETIC ELEMENTS, PHYSICAL LABORATORY. at 
The corrections which apply to the deflection observations are as 
follows: Correction for expansion of bar. This was obtained from 
the table sent out with the instrument from Kew, as were also 
those for temperature and induction, and it may be well to remark 
here that all observations were reduced to 0° and C G5 units 
are used throughout. The correction for distribution was 
obtained by taking deflection with the deflecting magnet at (a) 
30 cm. and (6) 40 cm. from the deflected magnet, this gives two 
M lap aN OR 
value of | whence a value of P, “the constant of distribution” 
' is obtained. 
The dip was measured five times inside the Laboratory and once 
out. It was found that the needle exhibited a tendency to stick 
on the agate ‘“‘ Knife edges,” however carefully these were wiped 
before the observation was begun. This appeared to be due to 
the condensation of a thin film of moisture and it was cured by 
putting a little phosphorus pentoxide into the box with the 
maguet whilst the observation was being taken. 
Observations of the declination were taken on two days and 
twice each day. The times adopted were at about 9°30 a.m. and 
2-30 p.-m., when the needle would be at its greatest western and 
eastern elongation respectively. Iam indebted to Mr. Knibbs for 
giving me the azimuth of a certain fiducial mark. This mark is 
about one and a half miles from the Laboratory, and is just on a 
level with the centre of the cross wires of the magnetometer | 
telescope when the instrument is set up over a plug on the land- 
ing at the western entrance to the Laboratory. 
Besides these, hourly readings were taken of the diurnal range 
in declination for a week both day and night, and the curves 
which accompany this paper are the result. For help on this 
rather irksome work I am indebted to Mr. J. A. Pollock and Mr. 
James Cook. 
In July 1890, Mr. J. W. Fell observed the horizontal force and 
in September 1888 Mr. C. A. Flint determined the horizontal | 
force and the dip. These observations are shown in the table, 
