SCIENCE OF COMMON THINGS. 233 



Use of a hole in the top of a lamp. Use of ground glass lamp shades. 



hot) rapidly ascends, driving the flame upwards at the 

 same time. 



1557* Why does the hand, held above a candle, suffer more from heat 

 than when it is placed below the flame, or on one side of it t 



Because the hot gases and air (in their ascent) come 

 in contact with the hand placed above the flame ; but 

 when the hand is placed below the flame, or on one 

 side, it only feels heat from radiation. 



1553 Why is not the wick of a candle consumed f 



The wick, although it is blackened by the heat, is 

 prevented from consuming, merely because it is sur- 

 rounded by inflammable vapor, so that the oxygen of 

 the atmosphere has no access to it. 



1559 Why do att closed lamps require a small hole in the top f 



To admit the air otherwise the pressure of the 

 atmosphere will prevent the oil from ascending the 

 wick ; if the hole be obstructed, the oil will sometimes 

 overflow from the expansion of the confined air. 



1560 Why do we use ground-glass globes for lamp shades ? 



To relieve the eye from the glare of light. Ground- 

 glass shades have the effect to disperse the rays by the 

 numerous reflections and refractions w T hich they occa- 

 sion ; until at length the light issues from all parts of 

 their surface, and it appears as though the glass itself 

 were the luminous body. 



CHAPTER III. 



RESPIRATION AND NUTRITION. 

 15 SI What is respiration? 



The act of inhaling air into the lungs, and again 

 expelling it. 



