280 WELLS'S NATURAL PHILOSOPHY. 



appearance of the inhabitants of these respective countries. Painters find that 

 their worli dries quicker, also, in New England than in central Europe. 

 Cabinet-makers in the United States are obliged to use thicker glue, and 

 watchmakers animal instead of vegetable oil. Pianos are rarely imported from 

 Europe into the United States, because the difference in the climate of these 

 two countries is so great, as respects moisture, that the foreign instruments 

 shrink, and quickly become damaged. 



whatissnow? ^l^- Siiow is tliG condcnsed vapor of the air, 

 frozen and precipitated to the earth. 



„ , Our knowledge in respect to the formation of snow in tho 



How is snow or , , , • 



probably form- atmosphere IS Very hmited. It is probable that the clouds m 



^^ ' which tlio flakes of snow are first formed, consist, not of vesi- 



cles of vapor, but of minute crystals of ice, which by the continuous condens- 

 ation of vapor become larger and form flakes of snow, which continue to 

 increase in size as they descend through the air. 



When the lower regions of the air are sufficiently warm, the flakes of snow 

 melt before they reach the ground ; so that it may rain below, while it snows 

 above. 



The largest flakes of snow are formed when the air abounds with vapor, 

 and the temperature is about 32° P. ; but as the moisture diminishes, and tho 

 cold increases, the snow becomes finer. 



In extreme cold weather, when a volume of cold air is suddenly admitted 

 into a room, the air of which is saturated with moisture, it sometimes hap- 

 pens that the vapor of the room will be condensed and frozen at the same 

 instant, thus producing a miniature flxU of snow. 



^ , . ,^ 617. On examining a snow-flake beneath a microscope, it is 



What is the „ , , • , , , • 



physical com- found to consist of regular and symmetrical crystals, having a 



position of a great diversity of form. 



Bnow-flake? ° ■' . i , j j ^ i 



These crystals also exist in ice, but are so blended together 



that their symmetry is lost in tho compact mass. 



The crystals of snow may, under favorable circumstances, be seen with 

 the naked eye, by placing tho flake upon a dark body cooled below 32° F. 

 Pig. 227 represents the varied and beautiful forms of snow crystals. 



The bulk of recently-fallen snow is ten or twelve times greater than that 

 of the water obtained by melting it. 



618. Hail is the moisture of the air frozen 



What is Hail ?.,-,. 



into drops oi ice. 



Can the phc- '^^^^ phenomenon of hail has never been satisfactorily ex- 



nomcnonofhail plained. It is difficult to conceive how the great cold is pro- 

 eatisflctorUy f duced which causes the water to freeze under the circum- 

 stances, and also how it is possible that the hail-stones, after 

 having once become sufficiently large to fall by their own weight, can yet 

 remain long enough in the air to increase to so considerable a size as \a 

 sometimes seen. A hail-storm generally lasts but a few minutes, very sel- 

 dom as long as a quarter of an hour; but tho quantity of ice which 



