70 GREENHOUSE CONSTRUCTION AND HEATING. 
of the (vertical) bars may be let (mortised) }in. or #in. into 
the transom and wall-plate ; but if this is done the tenons 
ought to fit very tightly, and the holes have a good dab of 
thick white (lead) paint, so as to prevent any soakage of 
water into the wood. Another way is to tack a strip of 
beading all along (if there is no rebate) first, then cut the 
ends of the bars with shoulders, and simply skew-nail each 
in its place. This may be done at both top and bottom. 
It is an excellent plan to champfer off the upper surface 
of a transom, on the inside, in order to prevent any lodg- 
ment of water, though this is seldom done. 
Where there is no door, the end of a comparatively low 
structure is simply filled in with light bars, fixed vertically at 
the right distances, as above. The 2in. by 1#in. is a useful 
size of bar for such work. In the absence of a door, a 
large hanging ventilator is frequently placed in the end of a 
span-roofed house. 
Remember, when nailing in the bars, whether in the roof 
or ends, that it is impossible to be too careful in fixing them 
at exactly the right distance apart. If too ‘‘tight,” great 
difficulty will be experienced in getting the sheets of glass 
in place, especially as one or two, a shade wider than the 
rest, are sure to be found here and there—this it is almost 
impossible to avoid—and if the bars are fixed at the bare 
width of the glass apart, there will probably be a lot of 
troublesome cutting to do, as well as great difficulty 
experienced in getting most of the glass in at all. If, on 
the other hand, the bars are put in too ‘‘wide” there will 
be too much play, and some of the squares will drop 
through altogether, causing a lot of extra trouble, and 
altogether preventing anything like sound work being made. 
