76 REPORT— 1842. 



ferent coloured fluids. Much delay has been occasioned in the observations 

 with these, owing to the difficulty of securing the contents in the glass cells 

 from leakage and evaporation ; the sun, the alkalies, and the acids acting on 

 the cements used to secure them. At length I have procured some very flat 

 flint glass bottles, which answer extremely well ; in these the fluids are about 

 an inch thick, and observe the following order in their absorptive actions : — 



A. Red. Solution of Carmine in Supersulphate of Ammonia. — This gives 

 a spectrum nearly in all respects similar to that given by the ruby glass (1) ; 

 all the rays above a line drawn through the centre of the space occupied by 

 the orange being cut off. 



B. Yellow. A saturated Solution of Bichromate of Potash. — This beauti- 

 fully transparent solution admits the permeation of the red and yellow rays, 

 which are extended over the space occupied by the orange ray in the unab- 

 sorbcd spectrum. The green rays are scarcely evident. 



From the absorptive powers of the sulphurets of lime and potash in solu- 

 tion, I was very desirous of using them, but they were found to be so liable 

 to decomposition when exposed to the sun's rays as to be quite useless for 

 my purposes, sulphuretted hydrogen being liberated in such quantities as 

 to burst the bottles with great violence. 



C. Gbeen. Muriate of Iron and Copper. — This medium is remarkably 

 transparent ; the blue, green, yellow and orange rays pass freely, all the 

 others being absorbed. 



D. Blue. Cupro-sulphate of Ammonia. — This fluid obliterates all the rays 

 below the green ray, those above it permeating it freely. 



E. White. — This is merely water rendered acid by nitric acid, for the 

 purpose of securing its continued transparency. It should be noted that 

 spaces in the cases have been left open to the full influence of the light, that 

 a fair comparison might be made between those plants growing under ordi- 

 nary circumstances, and the others under the dissevered rays. 



It will be seen from the above that the following combinations of rays 

 have been obtained to operate with. 



1 and A. The calorific rays, so called, well-insulated. 



2. A smaller portion of these rays mixed with a small amount of those 

 having peculiar illuminating powers. 



3. The central portion of the solar spectrum well-defined, and all the rays 

 of least refrangibility, thus combining the luminous and calorific rays, so 

 called. 



4-. The luminous rays mixed with a small portion of those having a calo- 

 rific influence. 



5. The most refrangible rays with a considerable portion of the least so ; 

 thus combining the two extremes of chemical action, and affording a good 

 example of the influence of the calorific blended with the chemical spectrum. 



6. Some portion of those rays having much illuminating power, with those 

 in which the chemical influence is the weakest under ordinary circumstances. 

 [Some information given me with great kindness by Sir John Herschel 

 shows that this is not a correct expression of the, case, as he has discovered 

 some preparations on which these rays act with the greatest intensity.] 



B. The luminous rays in a tolerably unmixed state. 



C. The luminous rays combined with the least actively chemical ones, as 

 in 6 ; but in this case the luminous rays exert their whole influence. 



D. The most refraugible or chemical rays well-insulated. 



E. White light. 



Although I have adopted the terms usually employed to designate the 

 divisions of the spectrum, yet it is necessary to bear in mind that these terms 



