28 THE ANTARCTIC MANUAL. 
interval of time. A knowledge of this change forms the only basis 
on which a closer investigation of the fundamental problems of ter- 
restrial magnetism can be founded. ; 
3. The Observing Stations, which, it is hoped, will take part in 
the international co-operation, are distributed over the globe with a 
uniformity never before attained. 
4. The Observations. All observations are simultaneous at all 
stations. They are of two kinds, viz. :— 
(a) Hourly observations of the three elements on certain fixed 
term days, to determine the diurnal variations of the 
Earth’s magnetism. 
(vb) Extended observations of the three elements during one 
hour agreed upon of each of the term days, to trace the 
course of individual disturbances. 
Observations of the first class begin at 0 h. pm, G.M.T., of a 
term day and end at 0 h. p.m. of the day following. At stations 
where the twenty-five hourly values of the three elements cannot 
be taken from the curves of self-recording instruments, readings of 
all three variation-instruments shall be taken precisely at each hour 
by three observers, but if only one observer is available the instru- 
ments shall be read successively as quickly as possible, in accordance 
with the following scheme :— 
(a—1) bh. 59 m. 308.G.M.T...  ..  .. Declination. 
Vertical force. 
Horizontal force. 
(x) h. 0m. 30s. ws ae ee) ee ~»=-d Horizontal force. 
Vertical force. 
Declination. 
Observations of the second class will, where possible, consist of 
photographic registers of all three elements taken on quickly-moving 
cylinders running for about two hours, with a wide time-scale (about 
twenty-four cm. per hour). At stations without the necessary equip- 
ment the variation instruments shall be read every twenty seconds 
for a complete hour, in the same manner as in observations of the 
first class, according to the following scheme :— 
(q)h. Om. Os. se ee ee) ee) Declination. 
Vertical force. 
Horizontal force. 
(x) bh. Om. 208. woes 4+ «+ Declination. 
Vertical force. 
Horizontal force and go on. 
(z@+1)h. Om. 038. «ae ee ee) Declination. 
Vertical force. 
Horizontal force. 
