EBULLITION. 



317 



Water, whether it exist in the state of liquid, in the state of steam, or in the 

 state of ice, is evidently the same substance, composed of the same elements, 

 and possessing properties in all respects the same, except in those mechanical 

 effects which are immediately connected with the three states just mentioned. 

 In fact, the state in which water may be found is a mere accident consequent 

 on the surrounding temperature ; nor can one rather than another state with 

 propriety be called the natural state of the body. 



If the expression natural state have any meaning, it must be that state in 

 which the substance is most commonly found ; and in that sense the natural 

 state of water in different parts of the globe is different. 



The variations of temperature incident to any part of our globe are included 

 within no very extended limits ; and these limits determine the bodies which 

 are found to exist most commonly in the several states of solid, liquid, and gas. 

 A body whose boiling point is below the lowest temperature of the climate, 

 must always exist in the state of vapor or gas, and one whose melting point is 

 above the highest temperature incident to the climate must always exist in the 

 solid form. Bodies whose melting point is below the lowest temperature of 

 the climate, while their boiling point is above the highest temperature of the 

 climate, will permanently exist in the liquid form. The permanent gases af- 

 ford examples of the first-mentioned class. Most solid bodies are examples 

 of the second ; and such fluids as mercury are examples'of the third. A liquid 

 whose melting point is a little above the lowest limit of temperature will gener- 

 ally exist in the liquid state, but occasionally in the solid. Water is an ex- 

 ample of this. A liquid, on the other hand, whose boiling point is a little 

 below the highest limit of temperature, will generally exist in the liquid form, 

 but occasionally in the gaseous. Ether, in hot climates, is an example of this. 

 Its boiling point is 98° ; and it could not exist, at certain seasons of the year, 

 in the liquid form, in India and other hot countries. 



Some bodies are at present retained in the liquid form only by the atmo- 

 spheric pressure. Ether and . rectified spirits of wine are examples of this. 

 If these liquids be placed under a receiver of an air-pump, and the pressure of 

 the air be partially removed, they will be observed to boil at the ordinary tem- 

 perature of the air ; whence it appears, that, if the pressure of the atmosphere 

 were considerably, less than it is, these substances would have existed only as 

 permanent gases. 



Great convulsions of nature, such as earthquakes, volcanic effects, and the 

 like, by which extraordinary quantities of heat are evolved, form exceptions to 

 this uniform state ; and the effects of such exceptions are discoverable upon 

 and beneath the surface of the earth : but, under ordinary circumstances, the 

 states of gases or airs, of liquids, and of solids, are determined by the condi- 

 tion just mentioned, namely, by the relation which their boiling and freezing 

 points bear to the extreme limits of the temperature of our climate. 



These considerations will lead us to perceive what would be the effect, if 

 the earth's distance from the sun were to undergo considerable change, either 

 by increase or diminution, other circumstances being supposed to remain the 

 same. If its proximity to the sun were increased, the increased influence of 

 solar heat would render it impossible for many substances now commonly li- 

 quid on the surface of the earth to exist in any other state than that of air ; 

 and, at the same time, many solid bodies would be incapable of maintaining 

 the solid form, and would become permanently liquid. It would be possible, 

 under such circumstances, that the water which now constitutes the ocean 

 would be changed into an atmosphere, and that many of the metals which now 

 exist in the solid form, distributed through the earth, would become liquid, and 

 fill the beds of the sea. If, on the other hand, the distance from the sun were 



