GLASS. 113 



dency to conduct the water to the centre of the pane, which is 

 let out by a small opening at the apex of it. If the lap is broad, 

 however, the water is accumulated by attraction precisely in the 

 point where it is calculated to do most injury, acting, in fact, 

 as a power on the end of two levers of the second kind. But 

 when the lap is not more than one sixteenth of an inch in width, 

 no evil of this sort can happen. 



It ought to be borne in mind that puttying, or otherwise fill- 

 ing up the laps, is in no case necessary if care be taken of the 

 glazing, and smooth glass be used, and if the lap never exceeds 

 one fourth, nor falls short one sixteenth, of an inch. However 

 careful the laps may be puttied, in a very few years the putty 

 begins to decay by absorption of moisture, and, when evapora- 

 tion is great within, it becomes saturated with water, which 

 readily freezes in frosty nights, (unless the temperature of the 

 house is adequate to prevent it,) and breakage of glass is inevi- 

 table. 



Reversed curvilinear glazing consists in making the lower 

 edges of the panes to curve inwards, in a concave form, instead 

 of curving outwards, in the common way. The effect of this 

 method is the throwing of the condensed moisture down upon 

 the bars, and thus conveying it off at the bottom of the roof, 

 which prevents the moisture from being retained in globules, 

 and dropping down upon the plants. This method is nothing 

 more than reversing the position of the panes in common curvi- 

 linear glazing, and is, according to our opinion, preferable to it. 



These are the most common and approved modes of glazing, 

 although some others have been used that have not proved 

 worthy of general adoption. Ridge-and-furrow roofs may be 

 glazed in the same way. The size of the panes used makes no 

 difference, large ones only tending to reduce the opaque sur- 

 face. Anomalous surfaces may be glazed with panes according 

 to the figures of the bars. 



. 



3. Color of Walls. The color usually applied to hot-houses 

 is white. As affording the finest contrast with the plants in the 

 interior, and the vegetation around the outside of the house, the 

 general taste is manifestly in favor of this color; and, as it is 



