320 



SCIENCE OF GARDENING. 



PART II. 



asserted, that green glass reflects off more than three fourths. Economy, as to the 

 quality of glass, therefore, is defeating the intention of building hot-houses, which is to 

 imitate a natural climate in all the qualities of light, heat, air, water, earth, &c. as per- 

 fectly as possible. Without a free influx of light, the sickly pale etiolated appearance of 

 plants is more painful than agreeable to the eye of any who take an interest in the 

 vegetable kingdom. As the panes or pieces of glass employed in hot-house roofs lap 

 over each other, the air which enters by the lap, when uneven glass is employed or care- 

 less glazing performed, no doubt, suggested the idea of closing the lap with lead or putty. 

 But both these modes being found to prevent the water which collects on the inner sur- 

 face of glass roofs, from escaping by the outside surface, gave rise, first, to partially 

 closing the lap ; and subsequently to various forms of panes, and descriptions of laps, of 

 which the principal are as follow. 



1627. Common sash-glazing is performed by even the best hot-house builders with a 

 lap of from one fourth to three fourths of an inch ; but by the great majority of glaziers, 

 with a full inch lap. The objection to this mode is, that the broader the lap, the greater 

 the quantity of water retained in it by capillary attraction ; and when such water, through 

 a deficiency of heat in the house, is frozen, the glass is certain of being broken. But 

 supposing this breakage not to take place, the broader the lap, the sooner it fills up witli 

 earthy matter, forming an opaque space, both injurious by excluding light, and unpleas- 

 ing because imperfect : or if the lap is to be puttied, the opacity is the same. The 

 accidental filling up of such spaces (when not puttied by art) with dust and earthy matter, 

 is what prevents them from being broken, by excluding the water in a great degree. 

 Where the lap is not more than one fourth of an inch, it may be puttied without a very 

 disagreeable effect. The rectangular pane is the only form which can with propriety be 

 admitted in curvilinear roofs ; and the most approved practice as to the lap, whether in 

 roofs or common sashes, is never to make the lap greater than the thickness of the glass, 

 and not to close it with putty. It is extremely difficult to get glaziers to attend to this ; 

 but by employing superior workmen, and obliging them to remove every pane which 

 shall project over the other more than one sixteenth of an inch, the thing may be accom- 

 plished. This is not only the most elegant of all modes for a curved roof, or indeed for 

 any other, but the safest for the glass, which is, we repeat, seldom broken by any other 

 natural means than the expansion of frozen water retained between the laps. It must 

 not be forgotten that this form is also by far the easiest to repair, and that no mode of 

 puttying or closing a narrow lap with lead is of long duration. 



265 



a b c d e f g 



1628. Glazing with a leaden lap (265. a) was formerly practised with a view of ex- 

 cluding the air by a more permanent material than putty. The sort of lap made use of, 

 is that used by glaziers in latticework windows (Jig. 266. a.) The panes being inserted 

 in the grooves, formed in the edges of the lap, are of 266 



course all in one plane, and the water in running 

 down either the outside or inside of the roof, must ac- 

 cumulate on the upper edge of each riband or cross- 

 string of lead, and so penetrate between it and the glass, 

 and drop on the plants in the house. This indeed 

 forms the chief objection to the leaden lap, which is 

 now deservedly exploded. 



.1629. An improved form of lead lap (Jig. 266. b) 

 consists in using slips of lead rolled so thin as not to 

 be thicker than fine drawing paper, in connection with 

 putty, and for the sole purpose of retaining it in its place. It is never allowed to project 

 beyond the exterior edges of the glass, so that it readily permits the descent of the water. 

 Its thinness renders it easily manageable, and the time employed in filling up such laps, 

 when one man is stationed outside the glass and another within, is not much more than 

 that occupied in glazing a roof with the common putty lap. Such lead laps may either 

 have a small opening in the middle, or at the angles, and are equally applicable to any 

 of the modes of glazing to be described. The lead is rolled to any width, and dipt or 

 cut to the size wanted as used. 



