HEAT AND MOTION, AND POLITICAL ECONOMY. 329 



are correlated with the development of microscopic organisms; this is 

 fermentation proper. The other set are dependent upon the action of 

 amorphous sohible substances ; this is diastasic fermentation. Now, 

 oxyo"en in a state of tension arrests the former class of phenomena^ 

 but in the latter class it is without any action. 



Thus we can entirely prevent the fermentation of must, the sour- 

 ino- of wine, the putrefaction of meat, etc., by means of oxygen in the 

 state of tension. This work once done, we may restore the normal 

 pressure, and then, provided germs from without are excluded, no 

 true fermentation will occur. 



I once hoped to be able in this way to preserve meats, eggs, etc., 

 but this was an illusion. The substances do not become putrid, but, 

 in consequence of a pseudo-fermentation, which sours them, they ac- 

 quire a disagreeable taste, which takes from the process all its indus- 

 trial value. 



At the close of this long discourse I would call attention simply to 

 one consideration. Atmospheric pressure acts a far more important 

 part in the life-conditions of organisms than is commonly supposed. 

 If we go back to the primordial geological ages, we may regard aa 

 highly probable the hypothesis that the pressure was then much higher 

 than now. This must be taken into account when we investigate the 

 origin of life. But, if we look to the future, it is plain that the press- 

 ure will go on steadily diminishing, just as the amount of water on 

 the earth's surface diminishes; and hence all living things are doomed 

 after the lapse of countless ages, it is true to perish by asphyxia 

 from the lessening of the atmospheric pressure. Hence the limits of 

 life upon the globe are fixed on the one hand by an excess, and on the 

 other by a lack, of pressure. Hevtie Scientijique. 



4 



HEAT AND MOTION, AND POLITICAL ECONOMY. 



THE law of the mechanical equivalent of heat may be summed 

 up in the following propositions, viz. : 



The heat required in order to raise a given weight of water one 

 centigrade degree of temperature can also lift the same weight 1,300 

 feet, or, more exactly, 424 metres. Thus to the unit of heat there 

 corresponds a definite amount of work. 



Conversely, a given amount of work produces also a definite 

 amount of heat ; in other words, there is required an amount of work 

 equal to 1,300 foot-pounds, in order to raise the temperature of one 

 pound of water one centigrade degree. 



Heat and motion, therefore, are convertible. 



Chemical processes are, in the last resort, the true sources of heat. 



