GREENHOUSES, HOTHOUSES, FORCING-PITS. 



255 



endless chain is to work and tm-n the screw, in fact, this is its axis. 

 The handle H is fixed to some convenient place on the front wall, being the 

 mover of the whole apparatus. As the rod is moved from right to left, the 

 short rods push the lights up and admit fresh air as they are acted upon : by 

 reversing the screw, the opposite result is obtained. 



689. The ridge-ventilation is obtained in precisely the same manner ; tho 

 lights under the coping being pushed out or drawn down by turning a 

 handle attached to a long endless chain on the end wall. 



690. The result of this system, to use Mr. Messenger's words, are,— 1. perfect 

 ventilation; 2. non-interference with the plants; 3. no risk of broken glass 

 by the lights fallen down ; 4. keeping out rain when the lights are open. 



691. The roof Mr. Messenger makes of very light rafters, only three inches by 

 two, strengthening them by means of a tension-rod placed under each, as shown 

 in the engraving. These are firmly fixed at each end, and kept extended by 

 means of two iron rods fixed in the rafters at equal distances from each other, 

 and from the extremities. Between these rafters sash-bars are placed, which, 

 when glazed and painted, are perfectly waterproof, and extremely light and 

 elegant in appeai-ance ; the tension-rods being both graceful, and the rafters 

 light and any, and strong enough for every purpose required. To his other 

 patents, Mr. Messenger has added a new principle of glazing for greenhouse 

 and other roofs which is perfectly waterproof and air-proof also without 

 putty. With this invention the roof may be nearly flat ; thus efiecting a great 

 saving in material, no paint being required in connection with it. 



692. The system of glazing patented by Mr. Messenger is simple and 



''^tn. 



ingenious : the upper surface of the sash-bar, of which 

 we give a section, is an open gutter, and the glazing is 

 pei-formed by bending the edge of the glass over the 

 edge of the gutter. The accompanying engravings will 

 make more clear the principle of this mode of glazing. 

 The gutters are made of either lead, copper, zinc, or 

 iron, or the sash-bar itself can be made with a gutter 

 on its surface. The mode of securing the glass down 

 to the gutter is shown by the section fig. 12. It is 

 done by a screw passing through a brass plate and India-rubber, into the wood' 

 or metal bar ; the India-rubber press- 

 ing slightly upon both sides of the 

 glass, keeps it in its place. If the glass 

 is very heavy, zinc or copper clips are 

 used to prevent it slipping down. 

 Fig. 13 is a plan of the roof, showing 

 the brass plates and shape of glass, 

 which is so arranged as to convey the 

 condensed vapour as well as the ex- 

 ternal rain into the internal gutter, 

 whence it escapes by a gutter attached to the wall-plate. 

 693. The cold and foi'cing pits are, of course, constructed on the same 



Fig. xxiu 



