ON THE CHEMICAL ACTION OF THE SOLAR RADIATIONS. 71 



(82) 1 6. The chemical action is weak, and the resulting Fig. 41. 

 impression after long development is far from strong. The 

 changes are, however, remarkable. In the very centre of 

 the yellow ray a faint spot is produced ; then all action 

 ceases until about '60 above a', a faint indication of che- 

 mical change again begins to be visible. This is continued 

 as a mere long oval stain, of pretty uniform intensity, to 

 rSO, when all action terminates. On the collodion plate 

 we have a very striking example of protective action, which 



is not apparent on the iodized paper ; and on the former W 

 preparation the action is continuous from the point at which ^, 



it commences to that at which it terminates. 



(83) I J. Deep yellow, /row, fig. 3, par. 8, First Rep. — The oblitera- 

 tion of the blue, the violet still continuing visible, is the most remarkable 

 characteristic of this glass. 



(84) 1 7. A slight indication of chemical change com- Fig- 42. 

 mences in the yellow ray, -18 above a'. This forms even- 

 tually a well-defined oval equal to '12; from this point ex- 

 tends a narrow neck, over which the chemical change is ^ 



exceedingly slight; then a well-defined oval extends to I'SO, 



with a slight interruption to its intensity and contraction at 



the extreme edge of the violet. Slight diSerences of colour 



are observable along this oval ; its general tone is a bright 



pure brown ; but where the blue rays should have fallen, 



there is a tendency to a gray ; and along the longitudinal 



centre of the image, it would appear as if some more ener- ^, 



getic power had been in operation. " 



(85) 18. Medium yellow. Charcoal, par. 6, First Report; and for che- 

 mical action on collodion plate, see fig. 21, which shows a most extraordinary 

 amount of action beyond the visible spectrum, par. 52. 



(85) 18. The chemical action on the iodized paper is Fig. 43. 

 limited to two well-defined spaces ; one, the most intense, a 

 dark oval over the point of greatest luminous intensity, 

 equal to '20, commencing at "15 above a' and terminating 

 at '35 a'. Between this point and the most refrangible 

 violet there is no effect, the paper remaining quite un- 

 changed ; then at the extreme verge of the luminous spec- 

 trum a weak chemical action commences, which extends to 

 1*20. This is singularly weak, except in the mean space 

 about -10 above a, where the influence of the chemical rays 



is more decided. 



(86) 67. High orange, Silver. — The luminous spectrum is nearly re- 

 duced to red and green, a faint line of yellow alone appear- . 



ing between these two ; the orange rays are completely ab- 

 sorbed, and the green losing much of its blue, appears of a 

 peculiar pale colour ; no rays visible beyond the green. 



(87) 6y. Although this chemical spectrum differs in some 

 respects from others already described, yet it exhibits pecu- 

 liarities which are, to a certain extent, common to all the 

 actions which have yet been obtained through yellow me- 

 dia. The chemical change commences and is most decided 

 in the yellow ray, where an olive-brown oval is rapidly 

 formed. At '70 above a' the second chemical change 

 occurs, forming a brown oval, which extends to 1*30. These 

 two ovals are connected by a very faint neck, which is only 



