KNIGHT'S VENTIIiATION-^WILLTAMS'. 225 



the external air was at 40°. This effect was produced b^ the heated air 

 being impelled into the body of the house amongst the plants, instead 

 of being permitted to rise, as it had previously done, and to come 

 instantly into contact with the roof: by suspending light bodies 

 amongst the plants, he ascertained that the previously confined air was 

 thus constantly kept in a state of rapid motion. The air was suffered 

 to escape through passages of four inches wide and two inches and a 

 half high, just below the junction of the roof and back wall, which 

 passages were placed at the same eq^ual distances as those in the front 

 wall, and, Uke those, were opened or closed as circiimstances required. 

 The trouble of opening or closing such passages, after substances of 

 proper form were prepared and. suspended for the purpose, was much 

 less than that of moving the lights of any house of ordinary construc- 

 tion; and the effect of the kind of ventilation obtained upon the 

 growth of his plants and fruit, was everything he wished it to be. 

 (For the plan referred to, see Physiological Papers, t, 7.) 



Another method, employed by Mk. Knight, was the following ; — By 

 passing pipes, open at each end, through the heating materials of a 

 hotbed, one end being in the interior of the frame, and the other 

 exposed to the open air, he succeeded in constantly renewing the 

 atmosphere of the frame, and in keeping the leaves in motion, with, as 

 he tells us, the happiest effect. 



Mr. Williams, of Pitmaston, pursued another course. He kept the 

 south end of his Melon-frame open to the outward air night and day, 

 except that it was covered over with a screen of " fly-wire ' ' painted black, 

 and continued in the inclination of the roof. This screen received the 

 rays of the sun from 10 a.m. to 3 p.m., all summer long; it became 

 heated to 80° or 100°, and consequently heated the air that passed 

 between its interstices. By raising the sashes at the back, a very 

 powerful current of air was established ; the thermometer ranged 

 from 80° to 90° below the leaves in a sunny day, and in short the 

 "atmosphere Was as hot as is experienced in the southern parts 

 of Italy, with almost as much ventilation as if 

 growing in the open air." — See Journal of Horti- sm 



cultural Society, vol i., page 43. The plan of "JR-c 



Mr. Williams might be modified by such a contrivance ^Q 



as is shown in the annexed section. Let A B repre-. // H 



sent a section of a front wall, or wooden frame ; C, a ^ M 

 hole ; D E F, a screen of zinc or iron, painted black, j,/_ ■ 

 nailed to it in front. It is obvious that when the ^H 



sun shines on the black plate, D B, it will rapidly g 



heat, and communicate its temperature to the air ^ 



below it ; the latter would immediately pass through ^'^" ^^^^i- 

 C, and with a, force proportioned to the elevation of its temperature. 



At DKATTOif Mange, the late Sir Robert Peel, with the advice, we 



4 



