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. 



Mr. Hunt also made a communication " on the Influence of Light on 

 the Crroicth 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 is in no 

 respect influenced by the acid element of the combination." To test 

 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, 

 an elevation of temperature occurred during the decomposition of its 

 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 



