94 Dr. H. T. Brown and Mr. F. Escombe. [Jan. 9 
Table VI.—Proportion of the Radiant Energy of Bright Sunshine Absorbed 
and Transmitted by the Successive Superposition of Three Leaves. 
Full unscreened radiation = 100. 




Radiation Radiation Rodianen ich 
NS eRe alae absorbed. transmitted. Wks a d ae 
ae ae Per cent. of | Per cent. of Na eae 
teal hell absence of selective 
absorption. 
Series A. Polygonum Weyrichii, 
coefficient of absorption, 
0:°647— 
One leat ies oehiotae: 64°7 35°3 a 
AWWiOr 1OaWES cscs ane tiak ss. 80°8 19°2 12-4 
Three leaves ........ aa 84°5 1525 4-4 
Series B. Helianthus annuus, 
coefficient of absorption, 
0:687— 
@Onesleatinwr ccc totes 68°7 31°3 — 
WOW CAVERStscsis Sc cose os 82°6 yf ae! 9°7 
Three leaves ............ 88°4 11°6 3°0 


The selective absorption of solar radiation by the green colouring matter of 
leaves, also comes out very clearly in certain experiments described by 
Timiriazeff, and referred to further on. He found, for example, that whilst 
the chlorophyll which had been dissolved out of a given area of a Maple leaf 
arrested 27 per cent. of the energy of direct sunlight, this absorption was 
only increased to 31 per cent. by a triple concentration of the solution. 
(d) Relative absorption of Solar Radiation by Albino and Green leaves of the 
same plant. 
The plant selected for these experiments was Negundo aceroides, and since 
the leaves were too small to be used with the Callendar’s radiometer in 
the manner already described, other means had to be devised for determining 
the coefficient of absorption of the leaf. The experiments were kindly under- 
taken by Dr. W. E. Wilson, and were carried out during the past summer 
at his Observatory at Daramona, Westmeath. 
In the first instance an attempt was made to employ the Boys’ radio- 
micrometer, by reflecting a portion of the sun’s image from a heliostat on to 
the suspended thermo-electric junction, and taking successive readings of the 
galvanometer with and without the interposition of the leaf-lamina. It was 
