301< Dr. H. Herwig's Investigations on the Conformity 



curve v 1 which will cut the curve Y Y twice ; i. e. the unit of 

 weight of vapour being enclosed in an invariable volume, may at 

 any temperature be perfectly saturated vapour; with an increasing 

 temperature it will withdraw itself from the superheated and 

 approach to the gaseous condition ; in this latter it continues for 

 a time under a still rising temperature, and under a higher in- 

 crease of temperature it again arrives at the superheated condi- 

 tion, indeed probably approaches this the more nearly the higher 

 the temperature is raised. Since, according to the mechanical 

 theory of heat, the temperature represents the measure of the 

 vis viva of molecular motion, while the greater or less deviation 

 of the vapour from the gaseous condition consists in a more or 

 less marked influence which the interaction of the isolated mole- 

 cules exerts on this motion, it must consequently be admitted 

 that the unit weight of vapour, when occupying an invariable 

 space, may, for a certain inertia of the molecular motion, display 

 a considerable degree of the maintenance of the molecular interac- 

 tion, which decreases as the motion becomes more active, entirely 

 disappears, and then, with a greater intensity of movement, reap- 

 pears and increases in energy the higher the molecular motion 

 is raised. 



This conception is difficult, it cannot be denied ; but the ob- 

 servations compel us thereto ; nothing else can be deduced from 

 the observations, even under the assumption of the widest pos- 

 sible errors in them. Moreover this conception appears to me 

 to be not at all inconsistent with the mechanical theory of heat. 

 For since the influence which the interaction of the molecules 

 exerts on their movement is measured by the quotient of the 

 time during which a molecule taken at random is found within 

 the sphere of action of other molecules, and of the time during 

 which it moves free therefrom, and since this quotient is a func- 

 tion, first, of the time elapsed during a single movement of two 

 molecules within their sphere of mutual action, and, secondly, 

 of the repetition of such meetings, therefore it is probable, con- 

 sidering the utter uncertainty in which we find ourselves concern- 

 ing the details of this occurrence, that at the commencement of 

 the above-described process the first moment especially, and at 

 the end the second moment come into account, while between 

 them there lies a condition when both moments are of impercep- 

 tible action. 



Very similar results are obtained from the consideration of Pj at 

 different temperatures, i. e. of the different tensions under which 

 the vapour at each temperature first enters into the gaseous con- 

 dition. Representing graphically the connexion of the tensions 

 p } and Pj with the temperature (fig. 3), the curve p x becomes 



