PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 497 



by absorption of heat rays, the kinetic energy of the oscillating aether 

 atoms is transformed into the kinetic energy of the oscillating particles: 

 in the radiation of heat by bodies, it is an inverted exchange of their 

 kinetic energies. 



A body whose atoms should tend to perfect repose would manifest the 

 absolute zero point of temperature. It has been calculated that the abso- 

 lute zero point, if it existed in nature, would be 273° C. below zero of the 

 thermometer. Although the absolute zero point of temperature does 

 not exist in reality, it is of value in the theoretical examination of the 

 heat theory. From the degrees of heat, calculated from the absolute 

 zero point, the absolute temperature is deduced. No gas is so perfect 

 that it could preserve its aeriform quality to near the absolute zero 

 point, but the most permanent gases even, would finally take a solid form 

 before the cooling process had reached 273° C. below zero of the ther- 

 mometer, notwithstanding that any degree of cold observed until now 

 in nature, or which could be produced artificially, lies very much above 

 the absolute zero point of temperature. 



As in reality there exists no absolute zero point of temperature, the 

 particles of all bodies in the universe as well as those of the universal 

 aether are constantly in a state of that peculiar motion called heat. In 

 solid bodies the molecules oscillate about certain centers of equilibrium. 

 If a solid body is heated, the oscillations of its molecules become more 

 rapid and extended, whereby its temperature and volume are increased. 

 The force of heat acts in opposition to the force of cohesion. By contin- 

 uous heating the force of cohesion may be rendered so feeble that the 

 molecules no longer oscillate about a certain point, but they move freely 

 among each other; it is then said that a solid body has become fluid, — it 

 has melted. 



By still increased heating of a fluid its cohesion may be so overcome 

 that the molecules with an accelerated motion scatter apart and disperse. 

 Freed from cohesion the vaporous or gaseous condition of substances is 

 attained. The gas molecules move always independently of each other 

 in a rectilineal direction until they strike other gas molecules or a wall 

 by which latter they are thrown back like elastic balls. The pressure 

 of a gas upon the surrounding walls is caused by the great number of 

 violently striking molecules. This theory of gases originated principally 

 with Daniel Bernoulli (1738), and was only recently applied very success- 

 fully to the mechanical theory of heat by Kronig, Clausius, and Joule. 



According to the preceding, the pressure of a gas if it be compressed 

 (supposing the temperature to be constant) and hence the corresponding 

 decrease of the volume of the same quantity of gas, must be proportional, 

 as it is evident that the shocks of the gas molecules on the walls will be- 

 come more frequent during each time-unit the more confined the space 

 is becoming in which the same number of gas molecules are moving. 

 (Boyle's Law 1GG0, or Mariotte's Law 1G83.) 



It will be easy to judge what process will take place in a body when 

 S. Mis. 54 32 



