
1905.] On the Physiological Processes of Green Leaves. 89 
leaves employed. Instruments of the type of the Angstrom’s compensating 
pyrheliometer, in which the radiation is received through narrow slits or 
diaphragms, to the almost complete exclusion of sky-radiation, are not so 
suitable for investigation of this nature. 
The radiometer was always exposed in close juxtaposition to the leaf, and 
in the same plane as the leaf-lamina, so as to ensure equality in the amount 
of energy received by the two surfaces. 
At the conclusion of an experiment, the integrated record, as given by the 
planimeter reading, was reduced to water-gramme-units of energy (calories) 
incident on one square centimetre per minute. 
As examples of some of the highest readings which we have obtained in 
this way in full sunshine, we may give the following :-— 
Table I. 
Solar radiation 
Date. ‘Time. in calories per square 
centimetre per minute. 
i a | 

July 10, 1900 ...... 4.0 PM. | O91 
iy etc 1220 , | 1-019 
June 2/7, 1901...... 20" 2; | 0°934 
PW y hey. tates: 2.20 ,, 0-941 
Shel 0 rere V0) eae | 0-932 



The observations above were made on exceptionally clear days, and with 
the sun’s rays normal to the receiving instrument. The values are somewhat 





Table II. 
Daaoneee Mean solar radiation : 
eee he et nn Percentage in calories per | 
i. hone of sunshine. | square centimetre per 
; minute. 
June 25, 1901......... 4°30 46 0:°246 
Ee ee | 2°54 100 0-479 
re ee 1°93 100 0-549 
BMT ty oka eon 0-90 70 0-393 
TS a ae 2°59 76 0-499 
By.) cxdisonees 1°55 100 0-550 
1°26 75 0°533 

