FORCING HOUSE tOR GRiPEt* {09 



consider as perfect; its application is by no meatis so: it 

 may nevertheless be a useful hint to those, who are engaged 

 iu very refined experiments on the nature of the metals, &c. 

 It would be less troublesome to construct, and perhaps more Another con- 

 applicable to most purposes, if made after the following ^J^^"^^'^*"^*^ 

 plan. Let A B be a glass cylinder, D the piston, and E E pose. 

 a plate of glass, large enough to cover the top of the barrel. 

 When this instrutnent is to be made use of, let the piston 

 be forced upwards, so as to project about a line or less 

 above the cylinder; let the glass plate E E (which must be 

 well ground to the top of the piston) be laid upon the pis- 

 ton, and let it then be drawn downwards; the plate will be 

 kept in its place, by the pressure of the atmosphere, (or 

 other means may be made use of to keep it more secure) and 

 the vacuum will be perfect, as in the former case. The glass- 

 E E may be made of a piece of common plate glass, if truly 

 ground; and the focus of the lens will easily be directed 

 through it, so as to fall upon the bottom of the piston. 



I am, Sir, 

 Your obliged and constant reader, 



L. O. C, 



IV. 



A Description of a Forcing House for Grapes; with Ohser* 

 vations on the best Method of constructing them for other 

 Fruits, By T. A. Knight, Esq. F, R, S, ^c* 



S 



O much difference of opinion prevails among gardeners Construction 

 respecting the proper forms of forcing houses, that two are o{ forcing 

 rarely constructed quite alike, though intended for the f^®"'*^ *'*' 

 same purposes; and every gardener is prepared to contend, 

 that the form he prefers is the best, and to appeal to ihet 

 test of successful experiment, in support of his opinion. 

 And this^ he is generally enabled in some degree to do» 

 because plants, when properly supplied with food, and 

 water, and heat, will succeed in houses, the forms of which 

 ar« very defective ; and proper attention is not often paj4 



• Tra'^.s. of the Horticultural S©c. Vol. I, p 9P -^ *♦ 



by 



