382 



PLANT-HOUSES. 



neatly jointed. As substitutes, we may 

 recommend Welsh and Irish slate, manu- 

 factured by Mr Beck of Isleworth and 

 others ; or ornamental tiles, of which the 

 Staffordshire potteries afford great variety. 

 For small greenhouses, tile quarries 6 

 inches on the side, in blue, red, drab, 

 and black, properly arranged as to colour, 

 will make a good and lasting floor. 

 Wright's quarries may also be used : these 

 on a pale yellow ground have dark brown 

 figures in pigment let in; or for houses 

 of the first order, Minton's encaustic tiles, 

 which can be procured in great variety of 

 design, and, if laid, will produce a very 

 splendid effect. Black and white marble 

 may also be employed ; but Minton's 

 tiles look better, and have a much warmer 

 appearance. The recent improvements 

 in the manufacture of slate by inlaying — 

 as shown by Mr Magnus in the Great 

 Exhibition — are worth the inspection of 

 those constructing houses of this descrip- 

 tion. In no department of horticultural 

 buildings is there more ample room for 

 still further improvement, both in respect 

 to elegance in form and adaptation to the 

 purpose for which they are intended, than 

 in the department to which we are at 

 present alluding. 



At page 114 we incidentally alluded to 

 the practicability of roofs of glass being 

 constructed upon the suspension prin- 

 ciple, with a view to enclose large spaces 

 without the necessity of using internal 

 supports; — we are now in a position to 

 prove the practicability of such a system, 

 and offer the following diagrams in sup- 

 port of our opinion. Before, however, 

 launching a principle so diametrically 

 opposed to present practice and opinions, 

 it may be necessary to preface our state- 

 ments with a few brief remarks. Suspen- 

 sion bridges — and those especially upon 

 Drench's principle — gave us the first idea 

 of a suspension glass roof. Bridges, in 

 principle of construction, may be consi- 

 dered a species of roofing, as each arch, 

 whatever be its form, is a roof over the 

 area it spans. For ages they were founded 

 upon the principle of compression, al- 

 though suspension ones may be traced to 

 a very remote date. Roofs, like bridges, 

 were founded nearly on the same data, 

 the compression at the ridge being coun- 

 teracted by tying the points of support 

 together, or, as is said in practical phrase- 



ology, guarding against the lateral thrust 

 which the base of all roofs has upon the 

 walls that support them. The difference 

 between compression and suspension— 

 where the material employed (as must 

 always be the case in hothouse roofs) is 

 of the lightest and least bulky form pos- 

 sible — is so great, that the following data 

 may be considered sufficient to prove the 

 correctness of the principle : — It has been 

 satisfactorily proved that a bar of iron, of 

 2 tons weight, and 1000 feet in length, 

 will sustain in a perpendicular position, 

 when suspended, 10 tons. A tower, for 

 example, upon the principle of compression, 

 of 1000 feet in height, capable of sustain- 

 ing the same weight, would require in 

 its construction more than one hundred 

 thousand times the amount of iron. On 

 the other hand, a bar of best iron, of an 

 inch area at the base, would sustain itself 

 on suspension nearly 60,000 feet in length. 

 Now, the same bar of iron would not 

 sustain itself in a perpendicular position 

 above 40 feet in length, apart from any 

 compressive weight being placed upon it. 

 The greatest power in nature is the ten- 

 sion or lifting power, and upon this all 

 suspension power is founded. 



Very lucid explanations and calcula- 

 tions, as to the stability of suspension 

 bridges upon Drench's principle, will be 

 found detailed in the " Surveyor's, En- 

 gineer's, and Architect's Journal ; " and 

 those who study the papers therein con- 

 tained will at once see the practicability 

 of suspending hothouse roofs in a similar 

 manner. Vibration and pendulous mo- 

 tion will be a different thing in roofs 

 constructed upon the ridge-and-furrow 

 principle from what it is in bridges, which 

 are long, narrow structures, as well as 

 subject at times to be loaded with very 

 great weights, which latter is the princi- 

 pal cause of that motion. Hothouses, on 

 the other hand — at least such as we 

 would apply the principle to — would be 

 of a different form altogether, their great 

 breadth constituting one of the causes of 

 the absence of vibration. Supposing a 

 hothouse to be 100 feet square, or 100 

 feet in length and 100 feet in width, the 

 vibration caused by the wind, which would 

 be the only power acting upon it to cause 

 a vibratory motion, would no more be 

 felt upon it than if the roof was supported 

 upon the compression principle — that is, 



