ON THE AGENCY OF SOLAR LIGHT. 
205 
habits, climate, and soil, ought, if possible, to be obtained, and studied as the 
basis of a wise system of culture ; but that success will chiefly depend upon the 
vigilant foresight (founded upon experience) of the gardener. What a system of 
education and observation does not this imply — and how ought men so educated to 
be rewarded by their employers ! 
This Paper is the favour of a highly respectable correspondent, and was received 
by us (as will be seen from its commencement,) shortly after the insertion of our 
first article on the ' Influence of Light.' The subjects to which it more particularly 
alludes, viz., the necessity of actual experience in the cultivation of plants, and of 
considering the obstruction which a glazed roof presents to the rays of solar light, 
are of the utmost importance, and had not been overlooked by us. We may, 
perhaps, be permitted a few further remarks on the latter of these points, for the 
former is too plain and palpable to require substantiating. 
In the construction of houses for the reception of plants, there can be no more 
serious error than that of omitting to take into consideration the angle at which the 
rays of light are most freely and directly transmitted, allowing more or less decli- 
nation to the roof, according to the aspect of the house, and the kinds of plants that 
are intended to be grown in it. To such an astonishing extent indeed is the light 
deflected by a glazed roof, that one which is constructed so flat as to render its 
inclination scarcely perceptible, is said to oficr an obstruction to light of at least 
fifty per cent. 
Gardeners too seldom allow this most vitally important circumstance due 
consideration, and as architects study rather the general appearance of such struc- 
tures than their adaptation to the cultivation of plants, the hot-houses of this 
country are frequently little better than places of shelter from the inclemency of 
the climate, instead of affording with the shelter every facility for the liberal 
admission of solar light. 
Those cultivators, however, who erect houses for the express purpose of growing 
any particular kind of plants which usually require some degree of shade, and think 
to incline the roof just so much as to render shading unnecessary, will be as 
egregiously in error as those who wholly neglect the subject ; for it is very easy to 
afibrd the plants any required degree of shading during the summer, but it is 
impossible to supply the deficiency of solar light in the winter, which would 
undoubtedly be requisite if the roof were inclined only to suit the plants kept in 
the house through the summer months. Besides, the purpose of shading is not so 
truly efi'ected by decreased declination of the roof, for in that case, the intensity of 
the light is only lessened by being wholly refracted, whereas, by interposing a 
denser medium, but at the proper inclination, some of the rays only are inter- 
cepted, while those which reach the plants are mitigated but not refracted, and 
consequently approximate nearer to the natural and desired method. 
The case of the fig-tree cited by our respected correspondent is very apropos ; 
