368 Scientific Proceedings, Royal Dublin Society. 
the stopwatch and marked the time when I considered the action 
completed to the usual colour, as it was of importance that the 
observer's judgment should be wholly uninfluenced by not knowing 
the previous watch-readings. We finished the observations at 
54 5m, as the tendency was an increase in the time of exposure 
with the Sun’s decrease in altitude. 
The quick rise in time of exposure at 5" 0™ was due to the 
Sun’s rays becoming parallel to the side of the building, in which 
was situated the window where the observations were made. 
GRAPHIC REPRESENTATION OF RESULTs. 
To represent these results graphically the observations were 
plotted to rectangular axes. ‘The ordinate of a point is the time 
of exposure in seconds required at the mean time represented 
by the corresponding abscissa. On describing the most probable 
curve satisfying these points, taking into account the state of the 
sky in estimating the value of each observation it was found to 
be of the form represented in fig. 1. This shows that, owing to 
the combined effect of the eclipse and the Sun’s decrease in altitude, 
the time of exposure increased rapidly from 52° at about 22 12”, 
represented by the point A, till about 3" 40™, when the time of 
exposure attained a maximum value 101‘, represented by the 
point B. After this a decrease took place till a minimum value 
86° was reached at 4" 26™, corresponding to the point C. It will 
be also noted that the rate of decrease B to Cis more rapid than 
that of increase from A to B. After 45 26™ the branch rises 
rapidly from C to D. According to the Nautical Almanac, the 
diclipse commenced at Be NES) 
Assumed greatest phase at 3 22 Dublin mean time ; 
Ended at 4 26 6 
thus the abscissee of the points A and C are coincident with the times 
of beginning and end of the eclipse, but Bis attained 18™ later 
than the moment of greatest phase. This was to be expected as 
the decrease in time of exposure, for a short time after 3 22™, 
due to the eclipse, would likely be counterbalaced by the increase 
due to the approach of evening. 
Depuction or ALtirupE Curve. 
To separate out the eclipse effect it was necessary to plot a 
