TERRESTRIAL MAGNETISM. 21 
poles, the weight on the needle being attached to the upper end of 
the needle as shown by the Dip. 
(6) Fox Dip and Intensity apparatus, or Fox Circle (in duplicate), 
for use at sea between any two land stations at which the absolute 
values of the Dip and Intensity can be observed. It is also recom- 
mended for use in sledging parties. 
(c¢) A special Standard Compass for observing the Declination or 
Variation at sea and for use in swinging to ascertain the constants of 
the disturbing iron in the ship. The two cards of this compass have 
periods of 23 and 15 seconds respectively ; the latter being provided 
for use in regions of low horizontal force. 
(ad) A gimbal stand for mounting the L. C. and Fox Circles and 
Fox Compass,* to be fixed in the centre of the ship’s observatory. 
(ec) Fox Compass. Horizontal vibration needle, and Vertical 
vibration needle in Dip circle, for ascertaining the disturbing forces 
of the ship’s iron at the centre of the ship’s observatory or ‘“ Fox 
position.” Also at Standard Compass position. 
Observations at Land Stations. 
It is considered that the Instructions given in the ‘ Admiralty 
Manual of Scientific Enquiry’ (1886), art. Terrestrial Magnetism, 
will suffice for the guidance to observers in the method of observa- 
tion and calculation of the results obtained by the Unifilar Magneto- 
meter, Barrow’s Circle, L. C. Circle, and Fox Circle at Land stations. 
Special instructions for the Eschenhagen Variometers will be 
supplied with the instrument. 
It is important that the magnetic survey in Southern waters 
should be preceded by observations at a base station at the Cape of 
Good Hope. The Cape Town magnetic observatory being disturbed 
by electric tramways, Simon’s Bay offers a satisfactory alternative for 
such a base station. Here the Absolute Horizontal Force, Dip and 
Declination should be observed with great accuracy and the Constant 
A for Lloyd’s needles on the Barrow’s and L. C. circles respectively 
determined. Complete base observations, including those for weight 
equivalents, should also be made with the Fox circles, 
On arrival at Melbourne immediate arrangements should be made 
for making complete observations with every instrument to be used 
in the survey at the Government Magnetic Observatory. This is not 
to include the Variometers, which are only intended for the extreme 
southern base. 
Especially should the Absolute Horizontal Force and Dip be 
* Special compass to be called tle Fox Compass. 
