DOUBLE GLAZING. 15 
and the under layer added for double glazing. All the 
difference in expense lies merely in the cost of the 
glass, which is a trifle compared with the use of two 
layers instead of one in early forcing. 
All good gardeners will doubtless see the advan- 
tages attached to the plan of double glazing, and I have 
Fig. 9.—SECTIONAL VIEW OF DOUBLE GLAZING, WITH SPRING BRASS CLI 
AND SCREW. 
As in fig. No. 7, but with rebate, letter a, rising one and a half eighth of an inch, 
' or the thickness of double glass, so that the edges can butt up to it, thus render- 
ing the glazing perfectly air-tight. The standards, aaa, need not be more than 
one-quarter of an inch wide, the screws, B, going through it. The under layer of 
glass is held in position by the thin metal clips, as in the illustration 2, 
no doubt that, if this is done without putty, or any 
other material that will prevent the water from con- 
densing into vapour, it will be seen at a glance that 
this method while perfectly air-tight is not retentive of 
water in the roof of the house, which when frosts occur 
materially lowers the temperature of the place. This 
is especially the case in single glazing, where extra fires 
must be kept up to keep out the frost. It is not 
necessary for me to say here that frost has a material 
