124 GREENHOUSE CONSTRUCTION AND HEATING. 
as ab B, in Fig. 79. The former would, at first sight, 
appear to be the better system, but in practice it has 
been found wanting, and all the best makers now 
fix their blinds by the second method. The great 
disadvantage of the first-named method is that a roller 
of more than a few feet in length is sure to ‘‘sag’’ more 
or less badly in the middle, under its own weight and that 
of the (possibly wet) blind, while there is no means of 
supporting it except at the ends. Then a multiplicity of 
short blinds and rollers is a thing to be avoided on several 
accounts, and lastly, the strain of several, or many, of the 
necessary brackets, fastened to the 
ridge, is frequently too much for 
this last, and causes it to give way. 
On the other hand, the roller 
is under the second method 
supported along every inch of its 
length by the blind itself—that 
is, if properly secured to it— 
and to some extent, also, by the 
bars, rafters, rods, or whatever it rests on. The actuating 
gear, or tackle, required by this class of blind is also more 
simple, as will readily be seen, than that of the other. 
In brief, the upper edge of the blind is nailed to the ridge, 
or rather to a batten fixed horizontally along the roof just 
below it (the ridge), the lower edge being secured to a light 
roller of wood or some other material, which is actuated 
by means of a couple of large plain pulleys or wheels, fixed 
one on each end, over which pass cords fixed to the ridge 
at one end and running over another pulley placed at or 
near the same point. The loose ends being drawn brings 
