Food for 

 Plants 



204 



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 his 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 suf 

 ficient 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 pendulum 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 

 would 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 equator 

 is 15,000 feet altitude; 13,000 feet between the tropics; and 9,000 

 to 4,000 between the latitudes of forty and forty-nine degrees. 



At a depth of forty-five feet under ground, the temperature 

 of the earth is uniform throughout the year. 



In summer time, the season of ripening moves northward at 

 the rate of about ten miles a day. 



The human ear is so extremely sensitive that it can hear a 

 sound that lasts only the twenty-four thousandth part of a second. 

 Deaf persons have sometimes conversed together through rods of 

 wood held between their teeth, or held to their throat or breast. 



The ordinary pressure of the atmosphere on the surface of 

 the earth is two thousand one hundred and sixty pounds to each 

 square foot, or fifteen pounds to each square inch; equal to thirty 

 perpendicular inches of mercury, or thirty-four and a half feet of 

 water. 



Sound travels at the rate of one thousand one hundred and 

 forty-two feet per second — about thirteen miles in a minute. So 



