OO REMARKS ON ARTIFICIAL CLIMATE. 



ing this loss by ordinary means, without adopting the unnatural 

 method of raising vapour by the direct action of the hot-pipe 

 either at a low or comparatively high temperature. The inevi- 

 table loss of moisture by condensation should be supplied by 

 natural evaporation from paths, and other available surfaces ; 

 but to meet the extra and more temporary demand occasioned by 

 bright sunshine in frosty weather, an immediate supply may 

 readily be obtained from the hot-pipes ; although, as is very 

 apparent, this last method is too artificial to be relied on for a 

 regular and genial supply of humidity. If ordinary care be 

 taken to keep the paths, &c., moist, it will be found that no very 

 injurious degree of dryness is produced even in maintaining a 

 minimum temperature of 60^ or 65° during frosty weatlier. In 

 large houses there will be less inconvenience felt from the loss 

 of moisture by condensation than in small ones ; and as preven- 

 tion is better than cure, small houses, or pits, should always be 

 covered with mats, or other suitable materials, thus preventing 

 loss of heat by radiation from the exterior surface, and conse- 

 quently loss of moisture by condensation on the interior surface 

 of the glass. The pine, and other forcing pits, and also the 

 smallest plant-stove here, which is span-roofed, 23 feet in height, 

 and 25 feet in width, are covered every night during winter, by 

 which a healthier atmosphere is not only preserved, but a great 

 saving is effected both in fuel and labour, and the cost of cover- 

 ing materials is amply repaid. 



Although, under the most careful management, this practice 

 must necessarily occasion some little loss of light, yet the loss is 

 but a trifling inconvenience compared with that of leaving 

 small houses uncovered during severe weather, for, as I have 

 already shown, it is difficult to regulate climate in the latter 

 description of buildings. Many plants are but little affected by 

 considerable variations in the degree of humidity ; but in all 

 unusual or difficult cases of cultivation, and also in early forcing, 

 during the flowering and ripening periods, culture of orcliids, 

 &c., more nicety will be required in regulating moisture, and 

 great variations in the amount of humidity will occasionally be 

 required to suit particular cases. Whenever any doubt exists on 

 this subject, Daniell's hygrometer should be used to ascertain not 

 only tlie real amount of vapour in the air, but also to test the 

 efficiency of our means of supplying any defect. I find no dif- 

 ficulty whatever in taking observations with this hygrometer at 

 any time, even by candlelight. When once the required degree 

 is ascertained, there will seldom be further need of consulting 

 this elegant, but somewhat delicate instrument, as two thermo- 

 meters, one with the bulb wet and tlie other dry, will give a 

 tolerably correct idea of tlie rate of evaporation, and indicate 



