42 AGRICULTURE 



wear lighter-coloured garments in summer 

 than in winter, the intention being to reflect 

 the sun's rays in summer and to absorb them 

 in winter. It may often be noticed, also, 

 that in warm districts the roofs of houses 

 are painted white in summer, the white 

 colour throwing back or reflecting the sun's 

 rays, many of which would be absorbed if 

 the roof were black or any other colour 

 but white. 



The great and immediate source of heat, 

 so far as soil is concerned, is the sun ; but 

 the temperature of soil is, to some extent, 

 influenced by heat directly received from 

 other sources, such as decomposing vegetable 

 matter. Every one is familiar with the fact 

 that a mass of farmyard manure especially 

 easily-fermentable material like horse manure 

 has a comparatively high temperature, 

 and this source of heat is utilized in gardening 

 practice in the propagation of plants in 

 frames. If the same amount of manure 

 were spread over a considerable area of 

 ground, one might be disposed to think that 

 it was providing no heat ; but, in point of 

 fact, the amount of heat given out during 

 its decomposition by, say, 10 tons of farm- 

 yard manure is precisely the same, no matter 

 whether it is concentrated below a garden 



