i>62 Intelligence and Miscellanies. 



den displacement of the air produces such a degree of cold, 

 as not only io freeze the vapour, forming the nucleus of the 

 hail, but to reduce the temperature of that frozen vapour far 

 below the freezing point. When therefore the warm air 

 comes in contact with this frozen vapour, the moisture is 

 precipitated upon it and freezes. In this way the hail is in- 

 creased as it falls to a very great size. 



Sometimes the temperature of the hail is so raised before 

 it reaches the ground, by the constant precipitation of moist- 

 ure upon it, that it is melted, and falls in extremely large 

 drops of water. 



5. Anthracite coal, and liquids, in quartz crystals. — The 

 students of Rensselaer school have, during the present sum- 

 mer, found numerous quartz crystals in the calciferous sand- 

 rock one mile north-easterly from this school, which were 

 terminated by six-sided prisms at each end, containing an- 

 thracite coal. They found two specimens which contained 

 a liquid, and one which has a piece of coal floating in the 

 liquid. — Prof. Eaton. 



6. Remarks upon the effect of a blast of air hetioeen con- 

 tiguous surfaces, in a letter to the editor dated West Point, 

 Sept. 4th, 1828. 



To the Editor. 



Sir — I beg leave to submit to your consideration an ex- 

 planation of the philosophical question relating to the two 

 Cards, since seeing the explanation in your last, I have tried 

 the experiment but cannot convince myself that the expla- 

 nation, there given, is satisfactory. It has been shown in 

 Nat. Phil, that " the force which a current of wind exerts 

 upon an inclined plane, varies as the sine of the inclination, 

 which the direction of the wind makes with the plane ;" 

 therefore, if the inclination is nothing, or if the wind passes 

 parallel to the plane, the pressure will be nothing. But 

 since the wind passes directly over the plane, it must re- 

 move the atmosphere from the space through which it pass- 

 es, and by its velocity, it will oppose a resistance to the pres- 

 sure of the atmosphere, which is exerted above it, and the 

 pressure on the surface over which the wind is blown, wilt 

 be less than the pressure of the atmosphere, and conse- 

 quently less than the pressure ou the other surface of the 



