?16 



CASSELL'S POPULAB, GARDENING. 



Fig. 40.— INDESTHTJCTIBLE WaLI-TKEE PhOTECTCJE. 



means of thin bent slips of zinc or copper, firmly 

 secured to the purUns, which may be either of wood 

 alone, or wood resting on angle iron, as is shown 

 in Fig. 38, where a represents the iron, B the fillet 

 of wood, c the zinc or copper clip, and d the glass. 



Fig. 39 shows a small 

 portion of a roof glazed 

 with 21 oz. glass. 



AAA, The top, mid- 

 dle, and bottom bars, are 

 made in 3 ft. lengths, of 

 either zinc or copper, and 

 are fixed with brass 

 screws to purhns or 

 bearers. The bars are 

 so constructed that all 

 condensed steam or va- 

 pour passes to the out- 

 side through the holes 

 marked a, on to the pane 

 of glass below. The top 

 portion of the centre 

 and bottom bars form a 

 series of clips and slots ; 

 the latter al- 

 low a free pas- 

 sage of water, 

 and the clips 

 secure the 

 glass in posi- 

 tion. 



B, Purlins 

 or bearers to 

 which the ho- 

 rizontal metal 

 bars are fixed. 

 These purlins 

 are two inches 

 in depth and 

 thickness, 

 more or less, 

 according to 

 the distance 

 the rafters are 

 apart. When 



the latter are more than four feet apart, 2 in. x 1 in. 

 X J in. angle-iron, with a fillet of wood fixed inside 

 (see Fig. 38) for screwing the bar to, will bear 6 ft. ; 

 2in. X IJin. xfin. will bear about 8 ft., which dis- 

 tance it is not advisable to exceed. Eafters made 

 4 ft. apart do not require angle-iron purlins. 



The purlins are best placed from 24 in. to 30 in. 

 apart if ^ glass is used, and up to 36 in. apart if -^^ 

 glass is adopted. When 21 oz. glass, which is the 

 best weight for all ordinary horticultural purposes, 

 is used, the distance should not exceed 24 in. 



c c. The glaas, is so cut that by pushing the top of 

 the square as far as it will go into the top bar, the 

 bottom edge drops over the cKps of the centre 

 or lower bars, and falls into its place, where it is 

 kept perfectly secure by the cUps. The squares of 

 ■-•^Ms arg' lapped verti- 

 cally from 1 in. to 1^ in. 

 according to the pitch 

 and position of the roof, 

 ^vhe^e they lie in close 

 contact with each other 

 and repel all water. 



D, Eafters. The rafters 

 or principals should not 

 be placed less than 3 ft. 

 or more than 8 ft. apart 

 for ordinary purposes. 



E, Shows the usual 

 method of forming the 

 ridge by fixing a zinc roll 

 to the ridge-piece, with 

 a flange sufficiently long 

 to overlap the top bar. 



One of the chief ad- 

 vantages 

 claimed for 

 this system is 

 the facility 

 with which 

 broken glass 

 can be re- 

 placed; there 

 is no hard 

 putty to hack 

 out, but all 

 that is re- 

 quired is to 

 secure the 

 broken glass 

 and to slip in 

 a new pane. 



The Wall- 

 tree TroUctor 

 (Fig. 40), con- 

 structed on 

 the same principle, will explain itself. It is con- 

 structed entirely of materials that will not wear out, 

 and is here introduced to illustrate the progress 

 which the removal of the tarifE on glass has 

 enabled to be made in the art of applying it to 

 horticultural purposes. The protector is supported 

 on iron brackets, which can be easily removed by 

 unscrewing the nut at the back of the wall. The 

 glass is fixed on the butt-joint principle, in the 

 patent bars, and can be removed, as all wall-treo 

 protectors should be when danger from spring frosts 



Eendle's Acme SrsTEai. 



Horizontal bar, constructed witli perforated chamiel to carry off any condensed 

 moisture from the inside, e, vertical bax, forming the junction of two squares of 

 glass. Tbe grooves carry oif any -water that may collect at this joint to the next 

 squEire below, and so on, from square to square. They also form a strong bearing 

 for the glass, g. Panes of glass. 



