212 



CASSELL'S POPULAR GARDENING. 



circumstances advantageous — became imperative, as 

 there is now no other means of keeping the air in 

 motion ; and ever}-^ practical horticulturist knows 

 how impossible it is to keep the tender leaves green 

 and healthy where atmospheric or exhaled moisture 

 is converted into scalding steam betwixt the foliage 

 and the roof. 



These difficulties have long since been overcome, 

 not only by early morning, "but by night ventilation. 

 Houses are built upon the best principles ; ventilators 

 of ample size are worked by machinery, and nothing 

 short of sheer neglect can result in scorching, scald- 

 ing, or burning. 



So far, the mode of applying glass to horticul- 

 tural purposes has kept pace with 

 the times. Even in these days 

 there is glass and glass ; but so 

 reasonable in price are now the 

 best qualities of British sheet that 

 it behoves horticultural builders 

 to use none but tlie best. For 

 many years 

 an immense 

 trade was 

 carried on in 

 Belgian glass, 

 and the Bel- 

 gian agents 

 in London 

 could under- 

 sell the Eng- 

 lish makers. 

 A change, 



however, has taken place in this respect, as British 

 manufacturers now produce an article at all times 

 reliable, at a price that will enable them to compete 

 with any nation in the world. 



Different Kinds of Glass.— Fifty years ago 

 the glass generally used in good gardens was 

 "Crown," of which many qualities were made ; but, 

 owing to the. mode of manufacture, and the cost, 

 small squares only could be used for horticultural 

 l)urposes. In many first-class establishments, where 

 expense was a secondary consideration, copper sash- 

 bars were us^d in preference to wood. The squares 

 were cut with elliptical ends, as shown in Fig. 31, 

 evidently for drawing the water away from the 

 sash-bars to the centre of the squares. Putty played 

 a very important part in this kind of glazing, as it 

 was used for bedding, facing, and filling in the laps, 

 a process by which more than ten per cent, of light 

 was excluded from the house, and many squares 

 were sjolit by expansion in frosty weather. In addi- 

 tion to this, the glass being extremely thin and fra- 

 gile, breakage during hailstorms was not unfrequent. 



Fig. 31. - Old Glazing. 



Sheet Glass. — The sheet glass of modem make is a 

 French invention, but the process of manufacture 

 has been greatly improved by English makers, and 

 the quality is now so good that it is universally used 

 for horticultural purposes. Besides, it is extremely 

 cheap, and, although less brilliant than crown, the 

 immense size of the sheets admirably fits it for en- 

 closing large areas. It is made in varying weights, 

 from 15 oz. to 21 oz., and 27 oz. per foot. The first 

 weight was at one time very extensively used, but 

 21 oz. has been found the most suitable for general 

 purpose^, and, strange as it may appear, protects the 

 occupants of a house from the efi:'ects of frost, where 

 they would often be injured under a roof composed 

 of glass of the lighter weight. 



It was with this kind of glass 

 that the fii'st Crystal Palace in 

 =- Hyde Park was glazed in 1851. 



Each sheet, 49 in. by 30 in., . was 

 cut into three panes, 49 in. by 

 10 in., and of these there were 

 300,000, mea- 

 suring over 

 1,000,000 

 square feet, 

 and weighing 

 400 tons. The 

 Palace at 

 Sydenham 

 has since been 

 glazed with 

 the same kind 

 of glass. 



IIartley''s Rough Tlate. — This glass was strongly 

 recommended by the late Dr. Lindley, and others, for 

 hot-house roofs, but it has not found favour generally 

 amongst fruit-growers. It is prepared by rolling, 

 a process which destroys transparency, without 

 diminishing translucency, and on this account it is 

 valuable for plant-houses, ferneries, and other 

 sti^uctures where the summer shading of sheet glass 

 is an expensive and troublesome affair. This, like 

 the sheet glass, has been gTeatly improved, and is 

 suitable for lofty roofs ; but owners of collections of 

 graceful plants object to it for side glazing, as 

 ornamental plants cannot be seen from the ex- 

 terior. Fruit - growers, too, in this .uncertain 

 climate, who force early and late, do not care to 

 use it. 



Polished- Sheet. — Where glass of very superior 

 quality is required for corridors or conservatories, 

 this will be found suitable. It is less expensive and 

 lighter than polished plate, and being prepared by a 

 process of grinding and polishing, it loses its original 

 wavy appearance, and acquires nearly all the beauty 

 of polished plate. 



Fig. 32.— Old Sash. 



