Heat and Organization. 165 



ternal work, and is given back when the body cools, and its 

 particles go back to their original state. Generally it happens 

 that adding any quantity of heat to a body does something 

 towards augmenting its bulk ; but there are some curious ex- 

 ceptions to this rule. Fusible metal, for example, expands in 

 cooling and solidifying, and if, after having thus expanded, it 

 is remelted by heat, its bulk is again reduced. " Water ex- 

 pands on both sides of 4° C. or 39 F. ; at 4° C. it has its maxi- 

 mum density. Suppose a pound of water heated from 3^° to 

 4f° C, that is, 1°, its volume at both temperatures is the same ; 

 there has been no forcing asunder whatever of the atomic 

 centres, and still, though the volume is unchanged, an amount 

 of heat has been imparted to the water, sufficient, if mechani- 

 cally applied, to raise a weight of 1390 lbs. a foot high. The 

 interior work done here by the heat can be nothing more than 

 the turning round of the atoms of water. It separates the 

 attracting poles of the atoms by a tangential movement, but 

 leaves their centres at the same distance first and last."* 



Very important consequences to life arise from the class of 

 facts just mentioned. 



If, for example, water did not consume a good deal of the 

 heat communicated to it in internal work, it would under solar 

 influence stow too hot for most of .the creatures that now 

 dwell in it. If a bowl of mercury and a bowl of water were 

 both exposed to a broiling sun, the former would become 

 unbearable, while the latter would only become tepid. 



For the comfort of the world it is necessary that water 

 should be able to keep comparatively cool, in spite of the 

 summer heat of the tropics ; but its constitution enables it to 

 do more than avoid an excess of temperature. It takes in 

 much more heat than is necessary to give it a proper degree 

 of warmth, and when cold weather comes, or when a warm 

 tropical current flows into cooler regions, -it gives back to the 

 air a quantity of its stored-up heat that is sufficient to make 

 climates temperate that would otherwise be frigid and severe. 



When an animal is exposed to a temperature much above 

 that which its solids and fluids could reach without destruction, 

 it escapes from getting too hot by setting the superfluous heat 

 to do another sort of work. It may, for example, evaporate 

 its fluids, and as they take a gaseous form, they absorb so much 

 heat in the internal work of separating their particles that no 

 mischievous augmentation of temperature can result. 



Numerous illustrations of these actions might be given. 

 One of the most interesting is afforded by Mr. Babbage, who 

 thus recounts his visit to Chantrey, when the sculptor had 

 heated a great oven for the purpose of drying the moulds of a 



* Tyiidall, p. 146. 



