THE REASON WHY. 43 



" And there are diversities of operations, but it is the same God which woi ketb 

 in all." CORINTHIANS xu. 



rounding air, at six to seven o'clock p.m. Other observations have 

 established differences of as much as 30 deg. between the temperature 

 of the spathe of the Arum cordifolium, and that of the surrounding 

 atmosphere. 



92. Have plants sometimes a temperature lower than that 

 of the surrounding air ? 



Yes. It has not only been found that under particular circum- 

 stances the heat of certain parts of plants is elevated to a very re- 

 markable degree, but that, under nearly all circumstances, they have 

 a temperature different from that of the external air, being warmer 

 in winter, and cooler in summer. 



CHAPTER VI. 



93. How many kinds of combustion are there? 



There are three, viz., slow oxydation, when little or no light is 

 evolved; a more rapid combination, when the heat is so great as to 

 become luminous ; and a still more energetic action, when it bursts 

 into flame. 



94. Why does phospnorous look luminous ? 

 Because it is undergoing slow combustion. 



95. Why do decayed tvood, and putrifying fish, look lumi- 

 nous ? 



Because they are undergoing slow combustion. In these cases 

 the heat and light evolved are at no one time very considerable. 

 But the total amount of heat, and probably of light, generated 

 through the lengthy period of this slow oxydation, amounts to exact- 

 ly the same as loould be evolved during the most rapid combustion 

 of the same substances. 



9G. Wliat is flame? 



It is gaseous matter burning at a very high temperature. 

 97. WTiy, when we put fresh, coals upon a fire, do we hear 

 the gas escaping from the coals without taking fire ? 



