378 DR. C. CHEEE; ANALYSIS OF RESULTS FROM THE KEW MAGNETOGRAPHS 
III all the figures, NS represents the astronomical meridian, MM' the mean 
magnetic meridian for the period, the two being inclined at an angle of 17° 18''8. 
The hours to which the individual observations refer are shown in the figaires, all 
being reckoned from midnight as 0. 
When N and W inequalities are not available, the vector diagram can he readily 
constructed by taking axes in and perpendicular to the magnetic meridian, employing 
for co-ordinates 8H and 8D, the latter converted into ab.solute measure. This was 
the method which I employed in tlie ‘ B. A. Beport ’ for 1895. 
The difihrence between the vector diagrams for December and June is very striking, 
the area described by the radius vector in the latter curve being about 16 times that 
descrilied in the former. The diagram for March pretty closely resembles that for 
the whole year, but encloses a somewhat larger area. In December the portion 
of the curve answering to the hours near midnight forms a regular closed loop—also 
seen in other midwinter months. The March curve shows a very tiny loop, and 
forms a transition to the June curve, where no loop appears, though the portion 
of the curve answering to the hours from 7 or 8 p.m. to 3 a.m. is still markedly 
indented. 
The longest radius vector, and so the largest value of the disturbing force, answers 
to about 1 P.M. in all the curves. The shortest radius vector answers either to about 
2 A.M. or 5 P.M. In all the curves the radius vector passes through astronomical 
south between 10 and 11 a.m., the time of crossing being somewhat earlier in 
December than in March or June. 
§ 30. Tlie second form of curve, illustrated by figs. 12 to 15, shows the change 
throughout the day in the direction of an imaginary magnet freely suspended as 
descril)ed in § 8. The curve may be supposed drawn by a style carried by the 
dipping end of the magnet, on a plane perpendicular to the mean position of the 
magnet throughout the day. MM' is the trace of the mag)ietic meridian in this plane. 
Fig. 12. December. 
