OBSERVATIONS ON THE ROOFING OF HOT-HOUSES. 
73 
convenient means for shading when necessary. What would the pine- 
grower do without the means of shading ? His plants would become 
stunted, contracted in volume, and yield smaller, though probably 
higher flavoured fruit. Hence a high and well lighted pinery is not 
so well adapted for the growth of pines, as a low and somewhat gloomy 
pit. In the native country of the pine-apple, as well as all other 
tropical plants, they cannot have more than twelve hours’ light, in the 
longest day of their summer, whereas, in this country, during the 
principal period of their fruiting, they enjoy from fourteen to seventeen 
hours’ sunlight, besides long twilights, which they do not have at home. 
And this may be one reason why pines, as well as other exotic plants 
require shading, in the middle of our summer days. It may be 
answered that, if tropical plants have more sun in our summer, they 
have less in our winter, and therefore there is something like equalisa¬ 
tion during the year. True: but as light is only one of the general 
influences received from the presence of the sun, and as we can supply 
the other by art, it does not appear that pines particularly suffer 
from want of sunlight during our short days. 
The object of the hot-house builder should therefore be to gain the 
morning light until eleven forenoon, and retain it as long as possible 
after three in the afternoon. And in the interval between these hours 
more shade should be thrown upon the plants, than there is before 
eleven and after three. This can only be done by opposing the opaque 
parts of the roof to the noon-tide sun, and placing the transparent 
parts so that the sun’s rays shall not pass through at right angles. 
That this has been accomplished by Mr. Paxton at Chatsworth, as 
well in a greenhouse lately built, as in the design for the conservatory 
intended to be built, we can affirm from a plan and elevation of the 
first, and from a model of the second, both of which we have seen and 
examined. Of this entirely new plan of roofing, we are in hopes of 
being able shortly to give figures in the Register, to be supplied by 
Mr. Paxton himself, but in the mean time we shall close this paper 
by some slight description. 
In order to give a faint idea of the construction of the roof, let us 
suppose that a hot-house is to be built in the common way, against a 
north wall of a garden, but to be covered with a Paxton roof (as we 
shall take the liberty to call it). Two sets of rafters, or principal 
bearers, are required; every other one being supported, say three feet 
higher than the intermediate ones. Of course there is, or may be, two 
plates, one three feet above the other in the back wall, into which the 
rafters are, or may be, dove-tailed for the better security of the building. 
The upper and under bearers are united by smaller ones, to bear the 
VOL. v.— NO. lvi. 
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