GLASS AND GLAZING, PAINTING, ETC. 81 
Tts superior lightness and strength are, however, important 
advantages, and it is doubtful whether the objection mentioned 
above is not more theoretical than practical. The area of 
bars, etc., presented to either the inner or outer surface, 
and through which alone the heat can be diffused, is 
comparatively insignificant, while the depth, or thickness, 
is per force considerable. Still, the theory is perfectly 
valid, and must be taken into consideration, especially in 
the case of stoves and forcing houses, etc., in which a 
temperature considerably above that of the outer air has 
to be maintained. 
Lengths of ordinary T iron may be easily substituted 
for the usual wooden rafters, or 
sash-bars, the glass being, of 
course, bedded in with putty, in 
the usual way (see Fig. 60). The 
difficulty lies, however, in finding 
a suitable method of fastening the 
squares down, tacks or brads being inadmissible, of course. 
Holes may, however, be drilled through the flange or rib of 
the bars, opposite the lower end of each square, a pin 
being inserted in each hole, and the glass secured by 
means of small wedges or cams; or small saddle-shaped 
spring clips, each with a screw on one side, may be 
employed, but the ends of these should be shod with leather 
or rubber, to avoid any risk of fracturing the glass. Or 
the glass may be easily fixed by means of lead clips encircling 
the lower part or ‘‘flat” of the bars, which are, of course, 
inverted thus—]. 
One large nurseryman in the north of London constructs 
most of his houses with JT iron bars, in a very similar 
G 
Fig. 60. 
