74 REPORT 1853. 



near which, around the edges, an action is again indicated by a colour some- 

 what different from that produced at the lower end. 



(97) 70. Yellow, hy Carbon. — This glass obliterates all the rays above 

 the green, and reduces the illuminating power of the least refrangible rays 

 very greatly ; the red rays alone pass the glass with tolerable intensity. 



(98) 70. An exposure to a very concentrated spectrum Y\%. 50. 



for three minutes is insufficient to produce any change „_ 



upon the iodized paper. By prolonging the exposure to 

 five or eight minutes, taking precautions to secure the fixed- 

 ness of the solar image, a space corresponding to the mean 

 yellow and the green rays becomes faintly coloured ; and 

 upon examination, even within this slight impression, varia- 

 tions in the intensity of action are apparent. 



(99) 73. Deep Yellow, hy Iron — The illuminating ^, 



power of the outstanding rays is very much reduced ; the • 



red, yellow, and green rays are alone distinctly seen ; the green passes 

 through various shades until it reaches a black, far up in the space previously 

 occupied by the blue rays. 



(100) 73. Chemical change commences at -70, and extends both upward 

 and downward from this point with nearly equal degrees of intensity, the 

 centre of action continuing well defined. At -50 above a! Fig. 51. 

 another action is established, and a similar well-defined spot 

 at -50 beyond a. Over the space occupied by the violet 

 and Sir J. Herschel's lavender rays, there is a space upon _ 

 which no chemical change takes place for a long time ; but 

 about ''2.0) beyond a a faint spot makes its appearance, which 

 is followed after a while by another a short distance above 

 it. This breaking up, as it were, of the spectrum into small 

 circles of chemical action cannot but be regarded as curious. 

 At present we are not in a position to offer any explanation 



of the phaenomena. At length the three principal spots be- ^, 



come united by continuous necks, over which, however, the 



chemical action is weak. 



(101) 76. Yellow, iy Cariow. — Red, yellow, and green Fig. 52. 



are the only colours of the spectrum which pass this glass, ■ — 



and these are considerably reduced in brilliancy. Beyond 

 the green, the space of the other rays is distinguishable 

 rather by its blackness in contrast with the other illumi- 

 nated spaces, than by any other indication. ^ 



(102) 76. We have here another example of the che- 9 

 mical action being confined to the most luminous rays ; the 



whole space darkened being equal to -10, and with the ex- a_ 



ception of some slight shading off" at the edges of the oval, 

 the colour is uniform. 



(103) 77. Yellow. — The blue rays are changed by the blending with 

 them of the red of the violet, which are but little altered. The green rays 

 are still visible, but they lose much intensity by the loss of their blue. The 

 yellow ray also suffers considerably in its intensity, and indeed the red and 

 orange are lowered in intensity. So that all the spectrum suffers rather in 

 its general illuminating power, than in any actual destruction of a particular 

 ray. 



(104) 77. The impressed spectrum in this instance bears a close resem- 

 blance to others obtained, after the incident beam has permeated yellow 

 media. At the least refrangible end the colour is an olive-brown, and an 



