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THE POPULAR SCIENCE MONTHLY. 



Had the lieat-rays which destroyed the ice fallen into water, it would 

 have been heated ; but, falling into the cube of ice, and melting a por- 

 tion of it, no change in temperature occurred. Ice melts at 32°, and 

 the temperature of the water'in which it floats is kept steadily at that 

 point until all of it has disappeared. The ices we consume, and the 

 iced drinks for which we thirst in summer, are, at the freezing tem- 

 perature, 68° colder than the internal organs wath wliieh they are 

 brought into contact. 



Ice, like other solids, may be cooled and warmed. That which 

 Tyndall chilled 100° could be warmed steadily to the temperature of 

 32°, and a thermometer would indicate the change ; but at that point 

 tlie jDrocess is interrupted — the structure falls into pieces, and not 

 until the mass is entirely liquid can the warming be resumed. From 

 that point, however, it goes on until, at a temperature of 212°, it 

 again ceases, and the molecules of water are separated into vapor. 



But, in melting the ice by the dark or heat rays of the beam of 

 light, a great quantity of heat was consumed, not in raising tempera- 

 ture, but in undoing what molecular force had done. To simply melt 

 a pound of ice requires 142° of heat, that is, an amount which would 

 raise the temperature of a pound of water 142°. Now, this is the 

 equivalent of the molecular force exerted in solidifying the water, and 

 the mechanical value of the two forces is the same. Expressed in fig- 

 ures, it is equal to lifting the same pound of ice 110,000 feet high. 

 The mere melting of 20 pounds of ice, a quantity received daily by 

 many families, is equivalent, in mechanical force, to lifting nearly 

 1,000 tons' weight a foot high, or to lifting two persons weighing 300 

 pounds 1,000 feet higher than the summit of Mount Washington. We 

 may thus realize the enormous display of energy along the line where 

 heat and molecular force contend for the mastery. 



The transition of water to ice, and of ice to water, produces impor- 

 tant changes in the temperature of surrounding objects. We are often 

 made painfully sensible of the chilling influence of the atmosphere 

 when its heat is rapidly abstracted in the melting of large masses of 

 ice and snow. But the reverse of this takes place in freezing. The 

 crystallization of water is attended with an elevation of temperature. 

 The heat which vapor carries with it in its aerial journeys is liberated 

 when those vapors are transformed into flakes of snow. The expres- 

 sion we often hear when a storm in winter is imminent, that " the cold 

 is too great for snowing," is true enough. The air is made warmer 

 when snow-flakes begin to form, and the temperature is higher than it 

 would otherwise be while snowing continues. In this way the forma- 

 tion of ice and snow modifies and softens the temperature of arctic 

 winters ; and the blossoms which open with the spring-time are not 

 more significant of milder airs than are those which are born of frost 

 and vapor, and expand their petals to the winter's tempest. Snow- 

 flakes are stellate in form ; the molecules of vapor in crystallizing 



