142 INTRODUCTION TO GENERAL SCIENCE 



temperature of any particular section of the air is not lowered 

 below its freezing point. Again, if there is much fog, there 

 will be no frost, since the formation of the fog raises the tem- 

 perature of the air. However, where the air Jias very little 

 water vapor, we may have what is called a black frost, which 

 merely means that the water in the plants themselves is actu- 

 ally frozen, and when this thaws out, they wilt and die. This 

 will explain the peculiar statement which people make, 

 namely, that after a cold night it is the sun which destroys the 

 flowers. 



References: 



1. 1103:290-291. Frost. 



2. 1304:246. Frost. 



3. Farmers' Bulletin No. 104. Notes on Frost, 

 a. 1101 : 135. Formation of Frost. 



6. 1102 : 156-158. Frost and its Prediction. 



c. 1301 : 132. Frost and its Formation. 



d. 1302 : 285-286. Dew and Frost. 



e. 1305:75. Hoarfrost. 

 /. 1306:108. Frost. 



g. 1310 : 367-368. Fog, Frost, and Cloud. 



h. 1311:227-228. Dew and Frost. 



i. 1312 : 381-382. Dew and Frost. 



j. 1807 : 199. Conditions for Frost. 



104. FOG AND CLOUDS 



These two are very much the same, the fog being either at 

 the surface of the earth or a little above it, while the clouds 

 are usually half a mile or more high. The conditions which 

 cause their production are very similar: a warm mass of air 

 carrying large quantities of water vapor is cooled, for various 

 reasons, which causes the water vapor to condense into a great 

 many minute drops which form the fog or clouds. 



