_ anelevation of temperature occu 
Proceedings of the British Association. 397 
shown that the changes are produced by a class of rays which lie be- 
tween the least refrangible blue, and the extreme limits of the violet 
rays of the visible prismatic spectrum—the maximum darkening effect 
being produced by the mean blue ray, whilst the blackening effect ap- 
pears to be produced with the greatest energy by the least refrangible 
violet rays. po 
Mr. Hunt also made a communication “on the Influence of Light on 
the Growth of Plants.” The peculiar influence exerted upon the ger- 
‘mination of seeds and the growth of the young plants by colored light, 
~ has been for some years the subject of the author’s investigations. ‘The 
results show the surprising powers exerted by the more luminous rays 
in preventing germination, and in destroying the healthful vigor of the 
young plant. Plants, when made to grow under the influence of the 
red rays, bend from the light as something to be avoided ; while the 
blue or chemical rays are efficacious in quickening their growth. It 
has however been found that although blue light accelerates germina- 
tion, and gives a healthful vigor to the young plant, its stimulating influ- 
ences are too great to ensure a perfect growth. The strength of the 
plant appears to be expended in producing a beautiful deep green foli- 
age; and it is only by checking this tendency, by the substitution of a 
yellow for a blue light, that the plant can be brought into its flowering 
and seeding state. The etiolating influence of the green rays was no- 
ticed, as well as the power which plants possess of sending out shoots 
of a great length in search of that light which is essential to their vigor. 
Dr. Andrews in a paper ‘“ on the Heat of Combination,” announced 
the general principle: ‘ When one base displaces another from any 
of its neutral combinations, the heat evolved or abstracted is always the 
same when the base is the same ; or, in other words, the change of tem- 
perature which occurs during the substitution of one base for another 
in any’neutral compound, depends wholly on the bases, and it 1s in no 
respect influenced by the acid element of the combina ; 
the accuracy of this principle by direct experiment, equivalent solutions 
of various neutral salts were decomposed by the addition of a dilute 
solution of the hydrate of potash. _When the strength of the solutions 
and their temperatures were properly adjusted, the same variation of 
temperature always occurred during the decomposition of salts of the 
same base. If the base (in the state of a hydrate) developed, when 
alone, less heat than the hydrate of potash in combining with the acids, 
yrred during the decomposition of its 
bination.”’ To test 
salts by the latter; if the reverse were the case, the decomposition of 
the salts was attended by a diminution of temperature. Thus the de- 
composition of equivalent solutions of the salts of the oxide of copper, 
was attended by the evolution of the same amount of heat, as was also 
ue #6 
* 
