57 
SOLAR LIGHT AND ITS AGENCY. 
Every fact that bears upon the inductive theory of vegetation ought to be collected 
and reported in a work like the present, as tending to exalt and verify its science. 
We (the writer of this article) cannot vouch for the impugnable correctness of the 
statements of which some abbreviated extracts will now be presented to the reader ; 
but, at all events, as the subject of scorching through the medium of the British and 
German sheet glass has been much canvassed of late, it will be interesting to recur 
to it, and to the remedy proposed. 
A paper was read by Mr. Hunt before the Society of Arts, on the 16th of 
February last, " On the principles upon which the tinted glass used in the construc- 
tion of the Royal Palm-house at Kew, has been selected, and the use of coloured 
media in the cultivation of plants." German sheet glass is distinguished by its 
freedom from colour, and has been found to produce scorching in particular solar 
aspects. " This has been observed in a striking manner in a hothouse for Orchids 
and Ferns, erected in the Kew Gardens." The phenomena alluded to were the more 
likely to take place when the medium through which the solar rays must pass was 
peculiarly transparent, and especially when the full power of the white, or combined 
rays, should thus freely act upon some plants which by nature are produced in dark 
and sombre recesses of tropical climes, wherein the atmosphere is vaporous, and 
tainted with the gaseous exhalations of decaying vegetable matter. 
Mr. Hunt commenced by stating that, " having furnished a report to the Com- 
missioners of Woods and Forests," he was requested to renew his experiments with 
a view to ascertain " whether any tinted medium would protect the plants from 
scorching, without interfering with those influences upon which their healthful 
vegetation depended." The Royal Palm-house is now glazed with such tinted 
glass. 
We have, on a former occasion, made some slight mention of the chemical 
principle of light, which has received the title of Actinism, evidently derived from 
the Greek word olkt\v, a sunbeam or flash of lightning. In describing some of his 
experiments, Mr. Hunt remarked that " the solar beam was now well known to give 
rise to three distinct classes of phenomena." These were, first, the production of 
colour and sense of vision ; second, heat, upon which depends the present condition, 
as regarded solidity or otherwise, of all terrestrial substances ; and third, a chemical 
agent, to which the name of actinism, or ray of power, had been given. 
If by power, the lecturer meant to imply the power to decompose or to form 
combination, he might be so far correct, otherwise the word has no reference to 
force of power in the abstract. 
" Physical investigation had made us acquainted with many of the laws regu- 
lating light and heat ; but in relation to photography few inquiries had been made 
VOL. XV. NO. CLXXI. I 
