IN POPULAR PHYSICS. 57 



55. Why can you heat water quicker in a tin than a 

 china cup ? 



Because the metal is a better conductor of heat than the 

 china. 



56. WJiy will a woolen blanket keep ice from melting ? 



The woolen is a non-conductor of heat. 



57. Does dew form under trees ? 



The trees reflect back the heat radiated by the earth, grass, 

 etc., and so prevent the temperature, in general, from sinking 

 to the dew-point. 



58. Wliat is the principle of heating by steam ? 



The steam is condensed in the pipes, and gives out as tem- 

 perature the energy which had been previously absorbed in 

 changing water to steam. 



59. IFJiat is the cause of " cloud-capped " mountains ? 



The warm, moist air from the valleys rises against the 

 mountain sides. Its vapor, previously invisible, becomes con- 

 densed by the colder air into a cloud of droplets that float in 

 the air. 



60. Show how the glass in a hot-house acts as a trap to 



catch the sunbeam. 



(See Physics, p. 259.) 



61. Does the heat of the sun come in through our ivin- 



doivs ? 



(See Physics, p. 259.) 



62. Does the heat of our stoves pass out in the same 



tvay ? 



(See Physics, p. 259.) 



63. TJie top of a mountain is nearer the sun; why is it 



not ivarmer ? 



(See Physics, pp. 250 and 200.) 



67. Can we find frost on the ivindows and on the stone- 

 flagging the same morning ? 



It requires a much intenser cold to produce the former ef- 

 fect than the latter, as glass is a poorer conductor of heat than 



