. The grape vine: its culture, uses, and history. hwhich they fall upon any given surface ; those whichfall upon it perpendicularly from the source of lightpass through with very slight diminution, but thosefalling upon it in a slanting or oblique direction arereduced in number in proportion to the obliquity ofthat direction. To ascertain how a glass roof maybe constructed, so as to receive the greatest numberof rays of light from the sun perpendicularly, or nearto perpendicularity at any given time of the year, itis necessary to know the latitude of the place wherethe hothouse is erected, and
. The grape vine: its culture, uses, and history. hwhich they fall upon any given surface ; those whichfall upon it perpendicularly from the source of lightpass through with very slight diminution, but thosefalling upon it in a slanting or oblique direction arereduced in number in proportion to the obliquity ofthat direction. To ascertain how a glass roof maybe constructed, so as to receive the greatest numberof rays of light from the sun perpendicularly, or nearto perpendicularity at any given time of the year, itis necessary to know the latitude of the place wherethe hothouse is erected, and the suns declination atthe period when most light is required. The latterinformation may be obtained from most almanacks,and if it be subtracted from the latitude, the remain-der will be the angle desired. If London be theplace, and May the 6th the time about when the mostlight is desired, the latitude being 51 degs. 31 min.,and the suus declension then 16 degs. 36 min. north, 15 therefore the roof ought to slope at an angle of 34(legs. 55 In latitude 52 degs., Mr. Knight found from length-ened experiments, that the hest angle is about 34degs., considering the services of a hothouse throughthe year; and to illustrate this, he gave the precedingdiagram. About the middle of May, the elevationof the sun at noon corresponds nearly with theasterisk, a ; in the begining of June, and early inJuly, it will be vertical at b, and at midsummer at c,only six degrees from being vertical. The asterisk,d, points out its position at the equinoxes, and e itsposition at midwinter. If the best glass be em-ployed, it is an excellent plan to have it put doublein each sash, an interval of half an inch being leftbetween the two panes, and a small hole at the cornerof the inner one to prevent the glass being broken 16 by the expansion or contraction of the air confined air is one of the worst possible conduc-tors of heat, keeping the house from being rapidlycooled during even the c
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Keywords: ., bookcentury1800, bookdecade1840, bookpubl, booksubjectviticulture
