382 First Report on the Experiments carried on 



for, on the same plan as in the other houses ; but the lights 

 are not fixed, because it is necessary for the perfection of 

 these fruit, both as to their colour and flavour, that they 

 should be exposed to the direct influence of the sun without 

 the intervention of glass, in the last period of their ripening. 

 These lights therefore have not been fixed, in order that 

 they may be taken off at the requisite time. 



Humidity in the houses. Some observations have been 

 taken with Mr. Dani ell's Hygrometer, upon the state of 

 the atmosphere in hot-houses; the result of which seems to 

 be this. That in curvilinear houses during the summer, the 

 degree of atmospheric moisture, which appears to be most 

 suitable to Tropical vegetation, may be settled to be about 

 .860, the temperature being from 80° to 87° Fahrenheit, 

 and the transmission of light such as has been already stated 

 to take place through an iron roof. And it has been satis- 

 factorily ascertained, that the nearer the temperature and 

 humidity of a stove, approximate to these degrees, the more 

 favourable is the artificial climate found for bringing the 

 powers of vegetation into vigorous action. It can also be 

 stated, that unless such a degree of humidity is carefully 

 maintained during the summer months in a hot-house con- 

 structed of iron, such a house will be found more rapidly 

 prejudicial to the health of plants, than one constructed of 

 wood, because its atmosphere if left to itself would become 

 more dry, and the plants would exhibit all the symptoms 

 consequent on aridity. 



Plant-pits heated by dung. In the Ornamental Experi- 

 mental Garden is a triple range of brick pits, heated ex- 

 ternally with dung, these have been erected upon a plan 



