CONSTRUCTION OF HOT-HOUSE ROOFS. 
83 
The elevation of the back wall is thirteen feet six inches^ at the lowest part, 
and fifteen feet at the highest part, or ridge of the angle; the height in front is 
eight feet six inches in the valley, and ten feet to the ridge of the angle. The 
lights of the roof (g) are made fast, and fixed on angle-fashion ; each light is 
twenty-five feet six inches long. All the front and end lights slide in a double 
groove (/t), so that, although there is no door, a person may enter at any part of 
the house. 
h 
The centre row of pillars (c) are two feet six inches longer than the front or end 
pillars ; about two feet from the bottom of each a small hole is left (z), through 
which a screw passes, to fasten the bearer which supports the centre walk (j). On 
the top of these pillars is also fixed another iron support (k), which is formed 
to rise up to the ridge of each 
angle; each of these arched 
supports have at their ends 
small square parts (Z), which fix 
in a hollow left at the top of 
each pillar im), and after being 
properly adjusted, they are fas- 
tened by running a little melted 
lead into the interstices. 
