INFLUENCE OF COLOUR 161 



The neighbourhood of large masses of water, by reducing 

 the severity of winter, tends to bring about an early spring. 

 Such situations are thus often extremely favourable for the 

 production of early crops, and are of great value to market 

 gardeners. 



Most striking are the differences of temperature determined 

 by the neighbourhood of cold or warm ocean currents. The 

 west coast of Scotland, and the coast of Labrador on the 

 opposite side of the Atlantic Ocean, are in the same latitude, 

 and receive the same solar radiation ; but the climate of the first 

 is so warmed by the gulf stream, and the prevalent westerly 

 winds, that fuchsias will live through the winter in the open 

 air ; while the temperature of Labrador is so reduced by a 

 cold arctic current that the sea freezes in October, and remains 

 in this condition until April. 



Influence of Colour. The amount of heat absorbed by a 

 soil when exposed to the sun's rays depends partly on the 

 colour of the soil. Schubler made the difference of colour as 

 great as possible by lightly sprinkling different portions of 

 the same soil with lamp-black, and with magnesia ; the soils 

 thus treated were then exposed to the sun towards the end of 

 August, and the maximum temperature reached one-eighth 

 of an inch below the surface was then observed. The black 

 soils under these circumstances became 13-! 5 F. warmer 

 than the white soils. The original character of the soil had 

 little or no influence on the temperature attained in this 

 experiment, provided all the soils were dry ; the colour had 

 clearly the preponderating effect. 



The excess of temperature shown by a darker soil depends 

 of course on the intensity of the sun's rays. Humboldt, 

 when in the Canary Islands, observed a difference of 25 F. 



M 



