374 Scientific Proceedings, Royal Dublin Society. 
This then is the relation which should hold between the magni- 
tude of the eclipse at any instant, and the actinic power of the 
Sun’s rays at the same instant. 
; ‘ " 1} 
The curve whose abscissa are the mean time, and ordinates — 
‘ Y 
as found from observations, was plotted and is the thick-lined 
curve shown in fig. 4 (p. 373). 
: S 
It was now necessary to determine the curve eh 
The Sun’s semi-diameter on May 28th, 1900, at mean noon, 
was 15’ 48-15”, and the Moon’s was 15’ 58°15” at the same time, 
according to the Nautical Almanac. We may then assume them 
equal. If 0 be the angle COP, fig. 5, which the line joining their 
centres at any instant makes with the radius of either to a point of 
intersection, we easily find 
S vy 
s w—20+sin 20 . 
Again, taking either radius to be unity, we have the distance 
between their centres 
OC = 2 cos 6 | 
and OM? = OC? —- MC: (9) 
