‘anhtel 
ON THE CHEMICAL ACTION OF THE SOLAR RADIATIONS. 267 

- other plants appear red on their under surface when examined through this 
giass, the light falling on the upper surface, and being trans- Fig. 17. 
mitted. Yellow Nasturtiums become of an intense brown. Blue 
Larkspurs not to be distinguished from the leaves. The violet 
and blue rays form a large oval, which, encroaching on the 
green, reduces it to a line bordering the lower edge of the blue. 
Yellow, a well-defined circular spot, ordinary red obliterated, 
and the extreme red forming a well-defined circular image quite 
surrounded by a black band. A prism of crown-glass gives 
the same result, as does also the hollow prism filled with Castor 
oil. The extension of this spectrum is remarkable. 
(39) 108. PALE GREY-BLUE appears to act most upon the 
yellow of natural objects, but produces no marked difference in 
the general tints. Its action on the spectrum is very slight; the yellow ray 
is somewhat reduced in size, and appears whiter than ordinary; and the 
green ‘is lessened by the blue ray encroaching on it. 
(40) 112. A smMoxy-BLUE.—No effect on colours generally; increases 
the extent of the violet and diminishes the blue. The yellow suffers, green 
passing into it; orange lost in the red. 
(41) 111. Biug-Grey.—Produces a slight, but by no means a marked 
change on the colours of natural objects; defines more perfectly the line 
between the blue and violet, and by lowering the yellow gives a more de- 
cided margin to the green. 
(42) 118. Pate BLUE, fig. 18—The reds of flowers are nearly Fig. 18. 
lost when observed through this glass, all extraneous light being —g—* 
shut off from the eyes. The red rays of the spectrum are thrown 
into two circles, and the yellow into a well-marked patch. The 
green rays are well defined; blue and indigo do not appear to 
suffer change. The red of the violet is completely lost. 
(43) 123. LicHT coBALT-BLUE.—The red of the spectrum is 
brought into a well-defined oval, the yellow very distinct; the green 
rays are considerably reduced. The blue rays extended, and con- a’ 
sequently the violet rays are much diminished. = 
(44) 47. Deep puRPLE GLAss.—Red, orange, green, and blue rays ad- 
mitted ; violet only distinguished after long examination. When concen- 
trated by a lens, the violet becomes quite visible as a well-defined band of 
coloured light. 


(E.) Miscellaneous. 
_ (45) 101. SMOKE-COLOURED GLAss.—Does not appear to alter the co- 
_ lours of natural objects observed through it. Blue of spectrum nearly ob- 
- literated, but the indigo and violet rays are extended; entire length of 
spectrum is not lessened. The most remarkable feature is the way in which 
_ the spectrum is extended over the violet end, proving the existence of red 
rays far down in the ordinary blue rays. 
(46) 106. A GREY GLAss.—Removes some red from the violet and 
shortens it. All the rays lose in luminous power, otherwise they do not 
_ appear, relatively, to change. 
_ (47) 115. SMOKE-COLOURED, HAVING A GREEN TINT.—Scarcely any 
action on either of the rays; there is a little loss of light. 
(48) 151. GLASS VERY SLIGHTLY sMoKy.—No change can be detected 
when this glass is interposed. 



