(32 THE EEASON WHY. 



" The light of the righteous rejoiceth, but the lamp of the wicked shall be put 

 out." PEOVERBS xm. 



were struck with the circumstance that the snow in front of the head-stones 

 facing the sun was completely dissolved, and, in nearly every instance, the 

 space on which the snow had melted assumed a coffin-like shape. This forced 

 itself so much upon our attention that we remained some time to endeavour to 

 analyse the phenomena ; and it was not until we remembered the curious effect 

 of reflected heat that we could account for it. It is obvious that the rays falling 

 from the upper part of the head-stone on to ihefoot of the grave would be less 

 powerful than those that radiated from the centre of the stone to the centre of 

 the grave. Hence it was that the heat dissolved at the foot of the grave only a 

 narrow piece of snow, which widened towards the centre, and narrowed again 

 as it approached the foot of the head-stone, where the lines of radiation would 

 naturally decrease. Such a phenomena would prove sufficient to raise 

 superstition in untutored minds. 



216. Are good reflectors of heat also good absorbers ? 



No ; for reflectors at once send back the heat which they receive, 

 while absorbers retain it. It is obvious, therefore, that reflectors 

 cannot be good absorbers. 



217. Sow do fire-screens contribute to keep rooms cool ? 



Because they turn away from the persons in the room rays of 

 heat which would otherwise make the warmth excessive. 



218. Why are white and light articles of clothing cool ? 

 Because they reflect the rays of heat. 



[White., as a colour, is also a bad absorber and conductor."] 



219. Why is the air often found excessively hot in chalk 

 districts ? 



Because the soil reflects upon objects near to it the heat of the 

 solar rays. 



220. How does the heat of the surfs rays ultimately lecome 

 diffused ? 



It is first absorbed by the earth. Generally speaking, the earth 

 absorbs heat by day, and radiates it by night. In this way an 

 equilibrium of temperature is maintained, which we should not 

 otherwise have the advantage of. 



221. Does not the air derive its heat directly from the 

 sun's rays ? 



Only partially. It is estimated that the air absorbs only one- 

 third of the caloric of the sun's rays that is to say, that a ray of 



