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XX VII. 
ACTINOMETRIC OBSERVATIONS OF THE SOLAR ECLIPSE. 
By SAMUEL ROBERT BENNETT, Scu. T.C.D. 
[Read June 20; Received for publication, Junz 29; Published Ocrozer 17, 1900.] 
INTRODUCTION. 
In order to determine the decrease in the Sun’s actinic power 
during the first period of the eclipse, 7.e. up to the moment of 
greatest phase, and the increase of the same during the second period 
(which were naturally to be expected to take place), the following 
experiments were made under the surveillance of Professor G. F. 
Fitz Gerald, F.R.S. It was to be anticipated also that the increase 
in actinic effect during the second period would be modified by the 
Sun’s decrease in altitude. But by eliminating the latter cause, 
the effect of the eclipse alone could be found. 
InstruMENT UseEp. 
The method adopted to measure the actinic effect at any 
instant during the eclipse was to have a piece of sensitised paper 
exposed to daylight, until darkened to a certain standard shade. 
This was effected by means of an actinometer. It consists of a 
circular disc of sensitised paper, enclosed in a light-proof case 
like a watch, one small sector of the dial of which is absent; so 
that a small piece of the paper can be exposed and compared with 
two standard colours, one on either side of this slit. 
OBSERVATIONS. 
By this means the following set of 54 observations were made, 
notes as to percentage of clouds and state of the sky being also 
taken. In the first column is given the mean time of the com- 
mencement of the exposure; in the second, the net time of exposure; 
and in the third, notes on the state of the sky, &c. 
