THE WOODWORK. 61 
Tt serves the double purpose of keeping the bars or rafters 
equi-distant and in their proper places in the middle, and 
also of supporting them at this point, and preventing any 
‘sagging ”’ of the roof from 
the weight of the glass, 
wind, or snow. A purline 
should always be supported 
at intervals of a few feet— 
6it. to 10ft., according to 
circumstances—by means of 
‘¢standards” of wood or 
iron. A purline increases 
the strength of the roof con- 
siderably, especially when 
the pitch is comparatively 
low. With a purline fixed FIG. 48. 
half-way up, a 3in. by 1Jin. sashbar will carry a roof 
up to 10ft. or even 12ft. of rafter capitally, even with 
2loz. glass, except, perhaps, in very exposed or windy 
places, when the 3in. by 2in. bars would be better and 
safer, particularly if wide squares of glass are employed— 
say over 15in. A portion of purline, with standards, fixed, 
is shown in Fig. 48. 
Where principal rafters are employed, no 
purlines are required, unless the rafters are 
very long indeed, though short iron bars are 
usually fixed between the principals, just to 
Bige dd: take the weight of the slighter bars. For this. 
purpose, lengths of angle-iron are very suitable, making a. 
very strong and neat job; a hole should be drilled opposite 
each sashbar, and a screw put in. In narrow houses, with 
