CHAPTER VII 
LIGHT AND HEAT 
THE ancients worshipped the sun as the source and giver 
of all good things. And so it is, for without its creating 
and sustaining energy this world would be a dead and 
tenantless globe, without sunshine and shower or any 
green and living thing. The energy of the sun’s rays is 
manifested to us under two forms : 
1. Light. 
2. Heat. 
The sun is always pouring into space streams of energy. 
These are transmitted as movements or undulations of 
the ether, a medium which is supposed to fill all space and 
penetrate all matter. The vibrations or undulations set 
up by the sun in the ether travel with incredible speed— 
186,000 miles per second—and in less than nine minutes 
traverse the vast distance (over 90,000,000 miles) which 
separates the sun and the earth. Light itself is invisible ; 
it is a sensation or form of consciousness produced in the 
brain by certain rays when they strike upon the sensitive 
nerves of the eye. Heat, on the other hand, is produced 
whenever the rays falling upon a material body are 
absorbed. What is really absorbed in this case is energy, 
and the rise in temperature is due to the increase of 
energy thus received. Since light, then, is a mode of 
consciousness, sunshine is only light to those that 
see. Plants cannot see. So far as they are concerned, 
the world is always in darkness, and what, in the day- 
time, is streaming upon the vegetation is not light, but 
energy. . 
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