ON THE INFLUENCE OP LIGHT ON SEEDS AND PLANTS. 77 



are not absolutely correct; Sir John Herschel has shown that the calorific 

 and the luminous spectra are co-extensive with the chemical one ; and my 

 own observations have proved that every ray of the prismatic spectrum 

 exerts a decided chemical action, the relative intensities changing with the 

 material upon which it is made to act. . 



These are matters of the first importance when the peculiar influences oi 

 light are to be studied, and it will be apparent from some of the results 

 which I have already obtained, that they demand the most rigorous investi- 

 gation. When we look on a spectrum which has been subjected to the 

 influence of some absorptive medium, we must not conclude, from the 

 coloured rays which we L, that we have cut off all other influences than 

 those which are supposed to belong to those particular colours Although 

 a blue glass or fluid-may appear to absorb all the rays except he most re- 

 frangible ones, which have usually been considered as the least calorific of 

 the solar rays; yet it is certain that some principle has permeated the glass 

 or fluid which has a very decided and thermic influence, and so with regard 

 to media of other colours. u„u:„,i 



The relative temperatures indicated by good thermometers placed behind 

 the glasses and fluid cells, which I have used, will place this ma clear light ; 

 the thermometers were carefully compared with a very excellent standard 

 one at the Polytechnic Hall, Falmouth. The following results present a fair 

 average series, and distinctly mark the relative degrees in which these media 

 are permeable by the heating rays :— 



Glasses. 

 Co l our . Rays not absorbed. Temperature. 



1. Ruby. Ordinary red, and the extreme red - |/° 



2. Red. Ordinary red, and orange, portion of extreme red. 8.3 



3. Orange. Little blue, green, yellow, orange, red, and ex- 



feme red. . . ^ 



4. Yellow. Red, orange, green, and blue. ...... »» 



5. Blue. Violet, indigo, blue, little green, and some red. 94 



6. Green. Orange, yellow, green, and blue <* 



Fluids. 



»7C0 



A. Red. Ordinary and extreme red ' ° 



B. Yellow. Ordinary red, and yellow «" 



C. Green. Blue, green, yellow, orange °» o 



D. Blue. Green, blue, indigo, and violet ' j> 



E. White. Green, blue, indigo, and violet by 



It will be found that these results are in strict accordance with those 

 obtained by Sir John Herschel. An interesting account of the thermic 

 spectrum, and the manner of obtaining it, will be found in a ;^cMe- 

 moir, Philosophical Transactions, Part 1 for 1840, page 51. \™«*$*» 

 a series of similar experiments on light, subjected to the analysing plates or 

 fluids, considering it highly probable that the various P**^**** 

 may indicate the condition of the calorific rays in a clearer manner than «e 

 can expect by the thermometer. „„„!„.• . 



There are some other points on which it is desirable to obtain conclu ive 

 experimental evidence, particularly with regard to the absorption oi other- 

 wise of the luminous spectrum, by the media through which it passes. 



The results obtained with the arrangements 1 have described are, up to 

 the present time, as follows : — . . 



. Bulbous and tuberous rooted flowers (tulips and ranunculuses) were 

 planted in pots, and placed in boxes under the glasses 1, 2, J, 4, b, b. 



