148 REPORT—1850. 
Green.—Muriate of copper and iron ;—blue, green, yellow and orange 
RRPRMPEEMEURS OPCEI Y's 7,5 cas iv τὰς okie neha v ka SN coeeee + 64 
Blue.—Ammonia, sulphate of copper ;—obliterating all the rays below 
Ce i τόκος plays ὡς Siegen) ἐχο τσ τα ΡΝ ἘΠ τς .... +100 
When the mark + is affixed to a number it indicates that the kind of 
action detected is positive, or belongs to the so-called chemical rays(actinism); 
on the contrary, when — is employed, the action detected belongs to that 
class which is associated with the least refrangible rays, or is of a negative 
order. ‘Thus, when the ruby-glass is employed, the chloridated photographic 
paper is very slowly changed to a red, as under the red rays; but in the case 
of the brown-red glass, an action, both positive and negative, is detected : 
the resulting colour is a gray; but if the spectrum is passed through such a 
medium, the impression is made at the two extremities of the spectrum + by 
the small portion of the blue ray which passes and — by the ordinary red ray. 
From these notices it will be seen to how large an extent we can succeed in 
separating the phenomena of the solar radiations from each other. Under 
one set of conditions, we can commanda large amount of light, which possesses 
no positive chemical power; while under another set, we can cut off nearly 
all the light, and admit freely the full amount of the chemical rays (actinism). 
Again, it must be remembered-that we can, as Melloni pointed out*, sepa- 
rate the luminous and calorific radiations very readily from each other. By 
the use of a green glass stained with oxide of copper, for example, a very 
large amount of the calorific rays are obstructed ; and I have found that a very 
slight tint of green is quite sufficient to stop those radiations which have been 
distinguished by Sir John Herschel as parathermic rays, and to which in all 
probability the browning of the autumnal leaves is due. From a series of 
experiments undertaken at the request of the Commissioners of Woods and 
Forests, I was induced to advise that a glass, stained slightly green with the 
oxide of copper, should be employed for glazing the Palm House in the Royal 
Botanical Gardens at Kew. This advice was acted upon; and as far as the 
opportunities of observing enable us to form an opinion, nothing can be more 
satisfactory +. 
A peculiar difference is found in the action of the solar spectrum on vege- 
table colours. This branch of the inquiry has particularly engaged the atten- 
tion of Sir John Herschel, and, notwithstanding the interesting nature of the 
inquiry, it appears to have been pursued by but one other experimentalist, 
Mrs. Somerville. 
It is proved that the chemical action of the solar rays upon all vegetable 
juices is confined within the limits of the Juminous radiations, no change 
having been detected over those dark spaces which are purely chemical and 
calorific. 
In the instance of gum guaiacum, it was observed by Dr. Wollaston, that 
paper washed with its tincture was changed to a blue or green by the most 
refrangible rays, and restored again to its original yellow colour by the least 
refrangible, which he regarded as due to the heat of those rays. M. Biot 
has shown that that portion of the resin soluble in water was not affected by 
the sun’s rays. These experiments have been confirmed by Herschel, who has 
however proved, contrary to the opinion of Wollaston, that the return of the 
colour was not due to heat alone; since beyond the luminous rays, where the 
calorific effect is at a maximum, no such change is produced. ‘“‘ Obscure 
* Bibliotheque Universelle de Genéve, No. 70, for October 1841. 
} On the Coloured Glass employed in glazing the New Palm House in the Royal Botanic 
Garden at Kew (Report of the British Association for 1847). 
