74 HEAT. 



the devious course of the river, or brooding over the 

 lake in the morning. 



169. NEWFOUNDLAND FOGS. The fogs 



What causes __ ,, , 



the Newfound- on the banks of Newfoundland are owing 

 land fogs? ^ Q ^ mixture of cold winds from the 

 north, with the warm air of the gulf stream, which 

 passes along that part of the ocean. 



170. CLOUD-CAPPED MOUNTAINS. The 

 402? ro- temperature of the air at high elevations 

 duced on high is always lower than at the general level 



mountains? 



of the earth. As the warm breeze comes 

 up from the warmer valleys, the two currents min- 

 gling, produce clouds. A clear atmosphere through- 

 out a whole day is rare, on high mountains. 



171. DEW POINT. It has been already 



What is the geen ^^ a j r ^as to be cooled more or less 



dew point ? 



before it yields moisture, according to the 

 amount which it contains. If it contains about one 

 cubic inch to the cubic yard, or, in other words, is satu- 

 rated, the least cooling will cause the appearance of 

 visible moisture. If it contains half as much, it must 

 be cooled down to 50 P. If it contains less than half 

 as much, still more refrigeration is required. The 

 temperature at which the deposition be- 

 gins in any case is called the dew point. 



172. HOW TO FIND THE 



How can the 



dew point be DEW POINT. - It is Common- 



ly found by adding ice, lit- 

 tle by little, to a glass of water con- 

 taining a thermometer. As the water 

 grows cool, the glass cools also, and as a 



