MR. WILLIAMS ON THE CULTIVATION OF MELONS. 



43 



inches higli,as soon as flie sun is on the glass, and not closed till 

 evening. This increases the indraught of air through the ■wire 

 screen, and I consider on every sunny day the melons are ex- 

 posed from 11 A.M. till past 3 p. m. to as hot an atmosphere as is 

 experienced in the southern paits of Italy, with almost as much 

 ventilation as if growing quite in the open air. 



I have grown Persian melons this way for some years past, 

 and obtained my bottom heat bj- tan and dry leaves, lining 

 the north or upper end of the bed with mowings of my grass, 

 weeds, &c. of the summer. But the bottom heat was often too 

 great in the early part of the season, an^ declined too low in the 

 latter part of the summer. Last spring, therefore, I adopted a 

 certain mode of giving bottom heat, which I contrived forty-one 

 years ago, when I made my grape-house : which is that of a 

 steam-vault under the soil in which tlie plants are intended to 

 grow. The steam-vault is formed by a brick arch ; the sketch 

 suj^poses an end section before the end is closed up by the brick- 



work of the frame, a, a, brick 9-inch wall ; h, b, the base of 

 the elliptic arch to hold steam ; r, the steam-pipe which con- 

 veys the steam from the boiler, d, holding five gallons, to blow 

 against the surface of the flat brick floor, and thus spread the 

 steam all over the vault instead of rising to the top of the vault 

 in the first instance ; e, the feed cistern with ball-cock on a level 

 with the boiler to supply it with water ; /', a small reservoir 

 which holds eight gallons, to supply the feed cistern. 



I find boiling the water for about two hours at intervals of 

 twenty-four hours, gives a certain heat to the soil above the 

 arch, and that the temperature of this soil always corresponds with 

 the quantity of water evaporated, as is shown by the sinking of 

 the water in the upper cistern. 



According to Watt, steam at the temperature of 212° occupies 

 1500 times as much space as when it existed in its liquid state. 

 I found that boiling the water for about two hours in twenty- 

 four, gave me in ordinary weather in summer, a ground heat of 

 from 78° to 82° or 83°, and that seven gallons of water were eva- 

 porated, as was shown by the loss of water from the upyjcr cistern. 

 Since loOOx T = 10,500, this number of gallons of steam must 

 pass into the \ault, and become condensed on the under surface 



