Food for Plants. 171 



Philosophical Facts. 



The greatest height at which visible clouds ever exist 

 does not exceed ten miles. 



Air is about eight hundred and fifteen times lighter 

 than water. 



The pressure of the atmosphere upon every square 

 foot of the earth amounts to two thousand one hundred 

 and sixty pounds. An ordinary sized man, supposing 

 Ills surface to be fourteen square feet, sustains the 

 enormous pressure of thirty thousand, two hundred and 

 forty pounds. 



The barometer falls one-tenth of an inch for every 

 seventy-eight feet of elevation. 



The violence of the expansion of water when freezing- 

 is sufficient to cleave a globe of copper of such thickness 

 as to require a force of 27,000 pounds to produce the 

 same effect. 



During the conversion of ice into water one hundred 

 and forty degrees of heat are absorbed. 



Water, when converted into steam, increases in bulk 

 eighteen hundred times. 



In one second of time — in one beat of the pendulmn of 

 a clock — light travels two hundred thousand miles. 

 Were a cannon ball shot toward the sun, and were it to 

 maintain full speed, it woud be twenty years in reaching 

 it — and yet light travels through this space in seven or 

 eight minutes. 



Strange as it may appear, a ball of a ton weight and 

 another of the same material of an ounce weight, falling 

 from any height will reach the ground at the same time. 



The heat does not increase as we rise above the earth 

 nearer to the sun but decreases rapidly until, beyond the 

 regions of the atmosphere, in void, it is estimated that 

 the cold is about seventy degrees below zero. The line 

 of perpetual frost at the ecpiator is 15,000 feet altitude ; 

 13,000 feet between the tropics; and 9,000 to 4,000 be- 

 tween the latitudes of fortv and fortv-nine degrees. 



