50 



Influence of Solar Radiation on Plants. 



The colored bell-glasses described in the previous Eeport were 

 made use of. I am now able to give a more accurate description 

 of what solar rays were actually transmitted by them. The 

 effects of the different glasses on the prismatic structum were as 

 follows : — 



Colorless glass. No perceptible difference from the normal 

 spectrum. 



Yellow glass. The red rays were cut off, but the line C was 

 just visible in the orange-colored region. The yellow and green 

 portions of the spectrum were quite natural, except perhaps that 

 they were rather more uniform in color than usual ; the blue was 

 rather bright above the double line F, but there was very little 

 illumination in the portion more refracted, and the violet rays 

 were quite unseen. The lines D, E, b and F were very visible. 



Red glass. The spectrum consisted of two luminous spaces, 

 separated by a broad band of perfect darkness. The one was of 

 a red and orange coJor, commencing between B and C, and appar- 

 ently cut off by the dark line D. The other was faintly illumi- 

 nated with an olive-green tint, commencing about the most 

 intensely yellow part of the ordinary spectrum, and continuing 

 to about b (which was barely visible), and then passing into a lilac 

 hue, which gradually faded off, till it became imperceptible per* 

 haps a little below the lines F. 



Blue glass. The spectrum had a very singular appearance, 

 consisting of several distinct luminous bands. First there was a 

 reddish band of considerable brilliancy, occupying a space be- 

 yond that of the least refrangible portion of the visible spectrum. 

 This was separated by a dark space from a very narrow but 

 bright band somewhere near the line B. Its color was very dif- 

 ferent from any of those of the normal spectrum, but perhaps it 

 approached nearest to the orange. Then, after another dark 

 space, came a bright yellow band of greater width, just above 

 the line P, which, however, was not itself perceptible. The 

 whole yellow portion of the spectrum was cut off, and there was 

 no illumination till about midway between E and 5, where a 

 bright green suddenly appeared. This passed into a pale green, 

 where there was very little illumination, but not perfect darkness, 

 till at about F an intense blue appeared, continuing through the 

 region of the violet, to the end of the most refrangible portion 

 of the spectrum. The lines b, F, and Gr were very distinct, as 

 well as some about d and H. 



This analysis of the light transmitted by the various glasses, 

 confirms the description previously given of their character, name- 

 ly, that "The blue glass cuts off by far the greater portion of the 

 luminous rays, but admits the chemical rays freely ; it may also 

 be considered as interfering much with the transmission of heat. 

 The red glass, on the contrary, freely admits the calorific influ- 



