74 
THE FLORIST. 
steam or water, and the space occupied by the warm air, previous to its 
condensation, is filled by the next body in rotation; there is therefore 
in cold weather a uniform motion of the heated internal air of forcing 
houses upwards to the glass roof, by coming in contact with which it 
becomes denser or is converted into water, according to the degree of 
cold to which it is subjected, and which of course depends on the state 
of the external temperature. 
The amount of radiation varies with the roof material used, being 
much more with metal roofs than those constructed with wood ; but as 
regards the amount of radiation from each kind of roof comparatively, 
we should say that the loss of heat, either by radiation or imperfect 
glazing, will be less from a roof constructed with a series of low ridges 
than from one with a uniform plane, for the reason that as radiation 
proceeds in right lines from all points of the surface exposed, these 
radiating lines will cross and obstruct each other when proceeding from 
a ridge and furrow roof, and by forming a warmer medium in the 
valleys prevent to some extent free radiation, and consequently less loss 
of heat. Again, the wind sweeping over the roofs of forcing houses 
soon lowers the internal temperature by extracting more rapidly the 
escaping heat as it passes from the roof. With the ridge and furrow 
roof we know from experience this does not happen to the same extent; 
the angular ridges into which this description of roof is thrown break 
the force of the current of air, and the temperature is not affected to 
the same extent as when the roof is formed in one plane. 
We will, in our next article, consider the questions of heating and 
ventilating, in reference both to first cost and efficiency and after 
working. 
(To be continued.) 
THE APPROACHING NATIONAL ROSE SHOW. 
The National Rose Show is at hand. As a lover of Roses I will do all 
I can to assist its views by subscribing, exhibiting, and imparting what 
knowledge I have to my fellow juveniles ; for of course I presume not 
to instruct 1 Mr. Rivers, Mr. Paul, and “ Wars of the Roses,” or 
even to approach them but with feelings of gratitude and admiration. 
I thank them heartily for their works and articles ; and I cannot 
refrain from commending a first-rate article on New Roses by Mr. 
Paul, in your volume of 1856, page 360 of the December number. 
Such articles will save me long journeys to Rose gardens. As all 
Roses for show should be put in directly, I will give my opponents in 
the Rose Derby a list of my kinds, many of which are excellent, if all 
are not first-rate, and some of which they will have to contend against. 
As Summer Roses are most delicate in colour, and as the French are 
full and good travellers, I will give their names first:—H.P. Blanche- 
fleur, Clementine ; M. Celina, White Bath ; G. Boula de Nanteuil, 
Grandissima, Kean, Latour d’Auvergne, Ohl, Schonbrun, Shakspeare, 
Triomphe de Jaussens. These are all shades of crimson, purple, and 
