514 NIGHT TEMPEEATUEE MUST BE 



and its accompanying refreshment are as necessary to them as 

 to animals. In all nature the temperature of night falls below 

 that of day, and thus one cause of vital excitement is dimi- 

 nished ; perspiration is stopped, and the plant parts with few 

 of its aqueous particles, although it continues to imbibe them 

 by all its green surface as well as by its roots ; the processes 

 of assimilation are suspended ; no digestion of food and 

 conversion of it into organized matter takes place ; and, instead 

 of decomposing carbonic acid by the extrication of oxygen, they 

 part with carbonic acid, and rob the air of its oxygen ; thus 

 deteriorating the air at night, although not to the same amount 

 as they purify it during the day. It is, therefore, most 

 important, that the night temperature of glass houses should 

 be lower than that of the day. We are told that in Jamaica 

 and other islands of the "West Indies, the air upon the 

 mountains becomes, soon after sunset, chilled and condensed, 

 and, in consequence of its superior gravity, descends and 

 displaces the warm air of the valleys ; yet the sugar-canes are 

 so far from being injured by this decrease of temperature, that 

 the sugars of Jamaica take a higher price in the market than 

 those of the less elevated islands, of which the temperature of 

 the day and night is subject to much less alteration. At 

 Fattehpur, in the East Indies, the difference in temperature 

 between night and day amounts to from 38° to 45° ; in April 

 the greatest heat by day is 110°, that of night is only 65°; in 

 January the thermometer falls to 38° at night, while the day is 

 76°; and there are 40 degrees of difference between the day 

 and night in May, one of the hottest months, when the ther- 

 mometer ranges as high as 115°. At Calcutta, in May, the 

 thermometer averages 93° in the day, and 79° at sunrise ; while 

 in January the temperatures are 77° and 56° respectively for 

 those two periods. 



But it is not merely in tte tropics tliat this great diminntioa of tem- 

 perature at night takes place ; it is universally the case in all climates 

 whence our fruit-trees have been derived. When we consider how 

 clear the sky is in the lands of the East, it is impossible that there 

 should not be a great amount of nocturnal radiation, the effect of which 

 ■will necessarily be to oool down the air to a very considerable extent, 

 especially in the spring. If we look to the registers of temperature 



