398 The effects of Light on the Germination of Seeds. 



least refrangible portion of the spectrum permeates this glass 

 freely. 



4. Yellow Glass. — This glass shortens the spectrum by 

 cutting off the extreme red ray, and the whole of the most 

 refrangible rays beyond the blue ray. 



5. Cobalt Blue Glass. — The spectrum obtained under 

 this glass is perfect from the extreme limits of the most 

 refrangible rays down to the yellow, which is wanting. The 

 green ray is diminished, forming merely a well defined line 

 between the blue and the yellow rays. The orange and red 

 rays are perfectly interrupted. 



6. Deep Green Glass. — The spectrum is cut off below 

 the orange, and above the blue rays, although the space on 

 which the most luminous portion of the spectrum falls ap- 

 pears as large as when it is not subjected to the absorptive 

 influence of the glass. There is a great deficiency of light 

 on a close examination with a powerful lens; a dark line 

 is seen to occupy the space usually marked by the green 

 ray. 



A case was also prepared, containing five flat vessels, filled 

 with colored fluids of various kinds, as follow : — 



A. Red. — Solution of Carmine of Supersulphate of Am- 

 tnonia. This gives a spectrum nearly in all respects similar 

 to that given by the Ruby Glass, (No. 1.) All the rays 

 above a line drawn through the centre of the space occupied 

 by the orange rays, are cut ofi". 



B. Yellow. — A Saturated Solution of Bicro7?iate of Pot- 

 ash. This beautifully transparent solution admits the per- 

 meation of the red and yellow rays, which are extended over 

 the space occupied by the orange ray in the unabsorbed spec- 

 trum. The green rays are scarcely evident. 



From the absorptive powers of the sulphurets of lime and 

 potash in solution, I was very desirous of using them, but 

 they are found to be so liable to decomposition when ex- 

 posed to the sun's rays as to be quite useless for such pur- 

 poses, sulphureted hydrogen being liberated in such quantities 

 as to burst the bottles with very great violence. 



C. Green. — Muriate of Iron and Copper. This me- 



