S TO 



561 



S T 



best way is to hnve no front putty at all. j most important property, when we con- 

 Instead of overlapping the panes as is '• sider that the healthy action of plants 

 done in the ordinary way, I cause the is in proportion to the quantity of light 

 glazier to cut each with a perfectly \vhich reaches them. The disadvan- 

 straight edge, and then to place them , tages of such roofs are, that they ra- 

 one before the other, so that they shall I pidly heat, and as quickly cool down; 

 all fit exactly. When the light is com- > they are therefore liable to sudden 

 pleted, the surface of the glass is per- changes of temperature, which can 

 fectly level, and there are no interstices only be guarded against by great atten- 



in which the dust, &c., can accumulate, 

 or for the oeposit of moisture. By this 

 means one cause of considerable break- 

 age in frosty weather is entirely avoided; 

 and if a pane of glass is accidentally i 



tion, w'hich is expensive, and by a large 

 consumption of fuel. We should say 

 use iron, if you prefer success and 

 beautiful form to cost, and can rely 

 upon the attention of your people, but 



broken, as each pane is independent of employ wood if you are obliged to study 



Fig. 158. 



the others, the fracture does not extend 

 beyond the single pane. The whole is 

 very firm and compact, and the glass is 

 not liable to shake out, as frequently 

 occurs in opening and shutting sashes." 

 — Gard. Chron. 



If lapping be permit- 

 ted, its width should not 

 exceed one-eighth of an 

 inch, and the panes 

 should be acutely rhom- 

 boid, to throw the con- 

 densed vapour down to 

 the lower corner, and 

 induce it to trickle down 

 the bars instead of drop- 

 ping. It is very doubt- 

 ful whether it reduces 

 the amount of moisture 

 taken between the laps 

 by capillary attraction. 



FlufS are best built of 

 bricks set on their 

 edges, and the top form- 

 ed of a shallow iron 

 trough for the purpose 

 of holding water, and 

 thus keeping the air 

 moist as required. At 

 night, for retaining heat, 

 pantiles may be placed 

 along within the trough ; 

 the best form is the an- 

 nexed. 

 Roof. — The framework of this may 

 be of iron or of wood, and the com- 

 parative merits of the two materials 

 are thus fairly stated by Dr. Lindley : — 

 " The advantages of iron roofs for 

 hot-houses are, that they are more dur- 

 able than wood, and allow a far greater 

 quantity of light to pass through them 

 than wooden roofs, the difference being 

 as seven to twenty-eight, or even 

 thirtv, in favor of iron, and this is a 

 '36 



Fig. 159. 



I 1 



economy." — Gard. Chron. 



Heating. — Flues for imparting heat 

 to hot-houses are for the most part su- 

 perseded by either tanks or hot-water 

 pipes; but where retained, the top 

 should be formed of iron plates, these 

 admitting the heat most readily into the 

 house, and consequently requiring a 

 less consumption of fuel. If it be de- 

 sirable to have covering for the flues 

 that will retain the heat longer, as 

 when the fires are made up at night, 

 this may be readily accomplished by 

 putting a row of the thick sijuare pav- 

 ing tiles on the top of the whole length 

 of the flue, an hour or two before the 

 houses are finally closed. 



The power of retaining heat, or in 

 other words of cooling slowly and gra- 

 dually, which renders the covering of 

 paving tiles desirable, renders the tank 

 system of heating by hot-water still 

 more efficient. It is a scientific opera- 

 tion throughout, and will be best appre- 

 ciated by a reference to Mr. Rendle's 

 diagram and description at page 500. 



It is a law of tluids that their hottest 

 portions rise to the surface of the con- 

 taining vessel, and the coldest portions 

 as invariably subside to the lowest sur- 

 face, because heat makes them expand, 

 and consequently diminishes their spe- 

 cific gravity; and the abstraction of 

 heat makes them contract, and as conse- 

 quently increase that gravity. When 

 the boiler and tank are filled with 

 water, as well as their connecting pipes, 

 and a fire is lighted, the hottest portfons 

 rise to the top, flow along the surface, 

 and getting cool, sink to its bottom, and 

 passing downward enter again at the 

 lower part, to be once more heated and 

 pass through the same circulatory sys- 

 tem. A very small boiler will speedily 

 raise the heat of the water, in a very 



