550 On the Influence of the Solar Rays on Vegetation. 



I think, then, that I may fairly conclude that the true tem- 

 perature of the sun is not very different from its effective 

 temperature, and that it is not much less than ten thousand 

 degrees if we only consider the absorption of the terrestrial 

 atmosphere, nor much more than twenty thousand degrees 

 if we also take into consideration the absorption by the solar 

 atmosphere, estimating the latter at -ffa of the total radiation 

 of the sun. 



LXIII. On the Influence of the Solar Rays on Vegetation. 

 By Robert Hunt, F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



AS the first publication of the results obtained by me, in 

 my investigations into the influence of the Solar Rays 

 on Vegetation, was in the Philosophical Magazine for April 

 1840, I hope you will allow me to remove a wrong impression 

 made by a paragraph in the Address of the President of the 

 British Association at Sheffield, and explain the reason of my 

 delay in doing so. 



Dr. Allman stated that Messrs. Draper and Pfeffer had 

 recently observed " that the solar spectrum is not equally 

 effective in all its parts " in its influence on the growth of 

 plants, thus leaving it to be inferred that this observation was 

 new with them. 



After the meeting (at which I was not present) I at once 

 (August 25th) referred Dr. Allman to my papers on this sub- 

 ject. These are to be found in the Philosophical Magazine, 

 as stated above, and in the Reports of the British Association 

 for 1842, 1843, 1844, and 1846 ; all of which were summa- 

 rized in my ' Researches on Light,' the first edition of which 

 work was published in 1844. I was favoured with a reply from 

 Dr. Allman on the 29th of August. After regretting that he 

 had overlooked my investigations, he adds, " I need not say 

 that I shall do all I can to correct the omission, and shall cer- 

 tainly take care that before the admission of the Address into 

 the Transactions of the Association due justice shall be done 

 to you in it." 



With this I rested content, until I received a letter from 

 Dr. Allman, dated November 9th, in which he writes, " I am 

 truly sorry to say that the Transactions of the British Asso- 

 ciation have stolen a march on me, and come out without 



