4 IQ 
n O R T I c 
Hof-houfes for the growth'of pistes feem not to have 
.been known in England at the beginning of the eigh¬ 
teenth century. Lady Mary Wortiey Montagu, on her 
journey to Conilantinople, itt the year 1716, remarks the 
.circumftance of pine-apples being' ferved up in the xle- 
fert, at the electoral table at Hanover, as a thing (lie had 
.never before feen or heard of. Had pines been then 
•grown in England, her ladyihip, who moved in the high- 
eft circles, could not have been ignorant of the fall. 
Hot-houles have hitherto been too frequently mifap- 
plied, under the name of Forcirtg-houfes, to the vain and 
oftentatious purpofe of hurrying fruits to maturity, at a 
feafon of the year when the fun has not the power of 
contributing any thing towards their natural flavour; we 
.have however begun to apply them to their proper ufe, 
and we have peach-houfes built for the purpofe of pre- 
fenting that excellent fruit to the fun when his genial 
influence is the moil adtive. We have others for the pur¬ 
pofe of ripening grapes, in which they are fecured from the 
chilling efFedts’of our uncertain autumns; and we have 
•brought them at daft to as high .a degree of perfedtion 
here, as either Spain, France, or Italy, can boaft of. We 
have pineries alfo, in which that delicate fruit is now 
raifed in a better flyle than is generally praCtiled in its 
jrative intertropical countries; except perhaps, in the 
.well-managed gardens of rich individuals, who may, if 
-due care and attention is ufed by their gardeners, have 
pines as good, but cannot have them better, than thole'”' 
,we know how to produce in England. 
The principal object in the conftru&ion of a hot-droufe, 
is indifputably that of forming its roof in fuch a manner 
as to receive all the heat it poflibly can from the rays of 
•the fun, and that at fuch fea'ions of the year when the ma¬ 
turation of the-fruit /lands moll in need of the folar in¬ 
fluence. This important objedl has by no means been 
unattended to by the ingenious Mr. T. A. Knight, who 
has favoured the public with the following interefling ob- 
fervations on the proper elevation which he thinks fhould 
;be preferred. It is fufficientiy evident, that, when the 
fame fruit.is to be ripened in the fame climate and feafon 
pf the year, one peculiar form for the elevation of the 
roof of the hot-houfe mud be fuperior to every other; 
and that in our climate, where funfhine and natural heat 
do not abound, that form, which admits the greatell quan¬ 
tity of light through the lead breadth of glafs, and which 
affords the greateft regular heat with the lead expenditure 
of fuel, mud, generally (peaking, be the bed; and, if the 
truth of this pofition be admitted, it will be very eafy to 
fhow-that few of our hot-houfes are at prefent well-con- 
ftrufied. 
“ It is well known, (fays Mr. Knight,) that the fun 
operates mod powerfully in the hot-houfe, wdien its rays 
fall mod-perpendicularly on the roof; becaufe the quan¬ 
tity. of light that glances off without entering the houfe, 
is inverfely proportionate to the degree of obliquity with 
which it ftrikes upon the furface of the glafs; and it is 
therefore important to every builder of a hot-houfe to 
know by what elevation of the roof the greatell quantity 
of light can be made to pals through it. To afcertain 
this point, I have made many experiments, and the refult 
of them has fatisfied rue that, in latitude 52,.the bed ele¬ 
vation is about that of 34. degrees.” 
On this elevation, therefore, Mr. Knight erefted his 
vinery, which, is forty feet long, and heated by a Angle 
fire-place; the flue pafling entirely round without touch¬ 
ing the walls ; and in the front a fpace of two feet is left 
between the flue and the wall, in the middle of which 
fpace the vine?, which are trained to the roofs, about 
eleven inches from the glafs, are planted; and, as both 
.the wall and flue are placed on arches, the vines are en¬ 
abled to extend their roots in every dircftion, whilfl, in 
ft he fpring, their growth is greatly excited by the heat 
which their roots and items receive from the flue. Air 
generally admitted at the ends only, where all the fafhes 
^,re made to llide, to afford a free paffage of air through 
U LTURl 
the houfe, when neceflary, to prevent the grapes becom¬ 
ing mouldy in damp l'eafohs. About four feet of the up¬ 
per end of every third light of .the roof is made to lift up,, 
(being attached by hinges to the -wood-work on the top 
of the back wall,) to give air in the event of very hot and 
calm weather. 
This plan is principally recommended for a vinery; 
but, by finking the front wall below the level of the 
ground, and making a fmall change in the form of the 
bark-bed, the.fame elevation of roof may be made equally 
applicable for the pinery. No upright front glafs ought, 
in any cafe whatever, to be ufed ; for light can always be 
more beneficially admitted by adding to the length of the 
roof, if that be properly, elevated; and much expence may 
be faved, both in the building and in fuel. Though this 
conftruclion is very favourable for grapes and pine-apples, 
yet Mr. Knight candidly acknowledges, it is not fo pro¬ 
per for the peach-tree. 
Improving on Mr. Knight’s idea of concentrating, the 
folar rays upon what fliall appear to be the beil poflible 
elevation of the roof, the Rev. Thomas Wilkinfon has 
publilhed the following ingenious Paper upon that fub- 
jefl, in the Tranfkftions of the Horticultural Society for 
1809. “Although it is probable that more depends on 
the 7 na?iagemcnt,*th. 2 .n on the inclination of'the roof, in any 
hot-houfe whatever, yet, as it is fatisfallory to proceed on 
fomething like principles, I endeavoured to afcertain why 
an angle of 34 0 was preferable to any other; which has 
led me to take a general view of the fubjeft. By point¬ 
ing out the times when the fun’s rays will be perpendi¬ 
cular to any conftruftion, and the reflection at the dif¬ 
ferent angles of incidence, we lhail be enabled to com¬ 
pare with fome accuracy the eftefls of the fun on differ¬ 
ent degrees of inclination, abllraftedly of internal ar¬ 
rangement, ftoves, flues, and culture. Now the angle 
contained between the back wall of the hot-houfe, and 
the inclined plane of the glafs roof, always equals the 
fun’s altitude, when his rays fall perpendicularly on that 
plane, provided that the inclination of the plane to the 
horizon be at an angle not lefs than 28° 4 , qor greater 
than 75 0 . The former is the cafe with moll cucumber- 
frames ; the latter with many pineries. It alfo follows 
that, within the above limits, the fun's rays are perpendi¬ 
cular twice in the year, once in going to, and once in re¬ 
turning from, the tropic. Hence then, having determined 
in what feafon we with'to have the moll powerful effects 
from the fun, we may conltruft our hot-houles accord¬ 
ingly, by the following rule. Make the angle contained 
between the back wall of fhe houfe and its roof — to the 
complement of latitude of the place, rh the fun’s declina¬ 
tion for that day on which we with his rays to fall per¬ 
pendicularly. Front the vernal to the autumnal equinox, 
the declination is to be added ; and the contrary. 
“To appiy thele principles to the conllruftion recom¬ 
mended by Mr. Knight, we have the inclination of roof, = 
34 0 . Therefore the fun’s altitude when his rays fall per¬ 
pendicularly is 56°, which, taking the latitude of London 
to be 5i°29 / , will happen when his declination is 17 0 31', 
about May 20, and July 21. Now we want the genial 
warmth of the fun mojl in fpring; and therefore, for gene¬ 
ral purpofes, that conftrultion would perhaps be. bell 
which gives us the greatell quantity of perpendicular rays 
then'. If the inclination were 45°, the fun’s rays would 
be perpendicular about April 6th, and September 4th. 
This conffruftion has the following limit: the height of 
the back wall mull-not exceed the width of the houfe + 
the height of the front wall. And, as the rays would 
vary very little from the perpendicular for leveral days 
before and after the 6th of April and September 4th, the 
lofs of rays arifmg from reflection would be nearly a mi¬ 
nimum. Even at the winter folltice, the lofs by'the ob¬ 
liquity of the angle of incidence, according to Bouguer’s 
Table of Rays reflected from Glafs, would be only two in 
one thoufand more than when the rays fall perpendicu¬ 
larly. But at the angle of 34 0 , the two days when thus 
Lays 
