102 The Transactions of the South African Philosophical Society. 
apparent local time to mean local time, and then, the longitude being 
known, to Greenwich mean time. 
The duration of annular eclipse also indicates, roughly, the breadth 
of the annular ring round the moon, for as the moon, on an average, 
moves thruugh its own diameter in sixty minutes, the ratio— 
Duration of eclipse: sixty minutes 
will indicate the ratio of the annular ring to the whole disc. 
The central path of the four most important eclipses, 
1940, October 1, 
1945, January 14, 
1954, December 25, 
1963, January 25, 
have been computed from Oppolzer’s ‘Syzygien Tafeln fiir den Mond ; 
and the central path of the other four, 
1900, November 22, 
1923, March 17, 
1934, August 10, 
1977, April 18, 
from constants given in Dr. Mahler’s ‘ Die Centralen Sonnenfinsternisse 
des XX Jahrhunderts.’ | 
The duration of eclipse, and the northern and southern limits of 
central eclipse, have been taken direct from Dr. Mahler’s work, as it 
was not considered worth while re-computing them from Oppolzer’s 
tables. The limits of central eclipse, and accordingly the duration of 
central eclipse, cannot be known with the same accuracy as the central 
line, inasmuch as they depend more upon the relative parallaxes and 
relative angular diameters of the sun and moon. 
At the commencement of each set of positions are the formule used 
in computing the central line of total or annular eclipse. 
In them, h = sun’s hour angle. 
@ = geographical latitude. 
X = longitude. 
