CH. VII.] THE FRUIT AND SEED. 223 



for the winds are then violent and diy even to a 

 proverb ; but it is during the days of its successor, 

 April, that sets in the only periodical wind, known 

 in this island. It comes intermittingly, and A-sith 

 variable force, from points ranging from e. to n.e., 

 and is one of the most blighting winds we have. It 

 continues until about the end of the second week in 

 May, though often until its close ; and it is a good 

 plan to have the trees during the whole period, by 

 day as well as by night, protected. This periodical 

 wind is occasioned, probably, by Sweden and Norway 

 remaining covered with snow, whilst England is 

 some 20° or more warmer; an upper current of warm 

 air is consequently flowing hence to those countries, 

 whilst a cold under current is rusliing hither to 

 supply its place. This wind, and its consequent 

 cold weather, is so regular in its appearance, that 

 in Hampshire and some other parts of England the 

 peasantry speak of it as " the blackthorn winter," that 

 bush being in blossom durmga part of its continuance. 

 Colour has very considerable influence over a body's 

 power of absorbing heat. If a thennometer on a hot 

 summer's day be exposed to the sun, it will indicate a 

 temperature of about 100°, but if the bulb be black- 

 ened with Indian ink, or the smoke of a candle, it 

 wiU rise from ten to twenty degrees higher. The ' 

 reason for this is, that the polished surface of the 

 glass reflects some of the sun's rays, but the blackened 



