-1859] WRITINGS OF JOSEPH HENRY. 119 



influences were brought to bear upon them. Let us further 

 suppose the sun to cease giving emanations of any kind into 

 space. The radiation from the earth, uncompensated by 

 impulses from the sun, would soon reduce the temperature 

 of every part of the surface to at least 60° below zero ; all the 

 matter and liquid substances capable of being frozen would 

 be reduced to a solid state; the air would cease to move, and 

 universal stillness and silence would prevail. 



Let us now suppose that the sun were to give forth rays 

 of heat alone; tliese would radiate in every direction from 

 the celestial orb, and an exceedingly small portion of them, 

 in comparison with the whole, would impinge against the 

 surface of our distant planet, would melt the ice first on the 

 equator, then on the more northern and southern parts of 

 the globe, and finally their genial influence would be felt 

 at the poles. The air would be unequally rarefied in the 

 different zones, the winds would again be called forth, vapor 

 would rise from the ocean, clouds would be formed, rain 

 would descend, and storms and tempests would resume their 

 sway. 



If the sun should again intermit its radiation all these 

 motions would gradually diminish and after a time entirely 

 cease; the heat given to the earth would in part be retained 

 for awhile, but in time would be expended ; the water would 

 slowly give out its latent heat and be again converted into 

 ice. Something of this kind takes place in the northern and 

 southern parts of the earth during the diff'erent periods of 

 summer and winter. Since the mean temperature of the 

 earth does not vary from year to year, it follows that all the 

 excess of heat of summer received from the sun is given off 

 in winter, and hence the impulses from this luminary which 

 constitute all the energy producing the changes on the sur- 

 face of the earth, merely lingering awhile, are again sent 

 forth into celestial space, changed it may be in form, but 

 not in the amount of their power. The solar vibrations have 

 lost none of their energy, for the water has returned to the 

 state of ice, and the surface of the earth is again in the same 

 condition in which it was before it received the solar impulse. 



