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of heat falling on a unit area would be less than E. Should, for 
instance, the surface lie at an angle of 45° to the incident rays, the 
area would be approximately 1.4. A, although there would be no 
increase in E, so that the amount of heat falling upon a unit area, in 
this instance, would be only about 70.7 per cent, of the maximum, 
1 
Fig. I. Relative amount of heat per unit area falling upon the soil whose 
surface lies at the various angles given to the incident rays. The maximum amount 
received is that of a surface which is at right angles to the rays, as is indicated in the 
figure. The direction of the incident rays is that shown by the arrow. 
that is, of the amount which would impinge on the surface were it at 
right angles to the source of heat. In short, it can be advanced that 
