82 KEV. G. HENSLOAV OX THE 



of moisture, cuHeris j^arihus, was most nl)uiidaiit in proportion to 

 the intensity of the lij^^ht admitted (orange <;lass iu ojeneral 

 causing more mois^tiire to be exhaled than red or green), yet in 

 some instances blue and purple glasses, and, still more remarkably, 

 bottles filled witli the cupreous solution [amnionio-sulpliate of 

 copper] Avould cause a more abundant exhalation than orange or 

 even transparent glass. Here, however, another principle seems 

 to come into play, nam^dy. the influence of heat radiated from the 

 surface of the screen " *. 



Deherain's researches alluded to above were made upon leaves 

 in a saturated atmosphere, and he came to the following con- 

 clusions, amongst others f : — 



'■' r*. L'evaporation de I'eau par les feuilles est determineepar 



la lumiere et non par la chaleur. 



*'2*^. Cette evaporation se continue dans une atmosphere 



saturee. 



" 3"*. Les jeunes feuilles evaporent plus d'eau que les an- 



ciennes. 



'' 4^ Les rayons lumineux ( jaune et rouge) efficaces pour deter- 



# 



miner la decomposition de Pacidc carbonique, sont aussi ceux qui 

 provoquent Tevaporatiou la plus abondante. 



it rt^ 



5"^. La difference d'action des divers rayons lununeux est 

 encore sensible quaud on s'efforce de les amener a une iutensite 

 lumineuse egale." 



The coloured fluids used by M. Deherain were as follows: 



"1. Dissolution rouge de carmiu dans rammoniaque. 



** 2. Dissolution jaune de chromate neutre de potasse. 



"3. Dissolution verte de chlorure de cuivre. 



** 4. Dissolution bleue de sulphate de cuivre ammoniacal. 



u K 



5. Dissolution violette d'iode dans le sulfure de carboue/ 

 The quantity of water " evaporated " in one hour by a leaf ot 

 Barley, reduced to percentages of the whole weight of the leaf, 

 was as follows : — Eed 93*G p. c, yellow 63'4, green 5'8, blue 63, 

 violet '05. 



The relative intensities of the rays, however, were not estimated 

 in any way. Nor were the lights tested by the spectroscope — a 

 most important and, in fact, necessary procedure ; as it is pretty 

 certain that they were not monochromatic J. 



♦ Phil. Trans. 1S3G, i. p. 160. t Ann. Sci. Nat. s^r. 5, xii. (1869)?. 23. 



I A violet glass of a peculiar reddish tint in my possession transmits ihf 

 whole of the spectrum^ and is therefore useless for experimental purposes. 



