1881.] 4j5 [Chase, 



group. If 208 is its true value, it should be excluded from the first two 

 groups. All these arrangements are, for the present, only tentative, but 

 I think that an increase in accuracy of determination will be more likely 

 to increase than to diminish the number of indications of this kind. 



My anticipation of a "ponderable disturbance of equilibrium, which 

 must give rise to sethereal oscillations in every chemical action," was pub- 

 lished in 1864*. The confirmations of that anticipation, by Cooke, Men- 

 delejefli', Meyer and others, lead me to hope that a careful consideration of 

 the common factors in different supposed elements will help towards further 

 analysis and, perhaps, towards the final discovery of the laws by which 

 all chemical substances are developed from a single primitive form of 

 matter. 



55. A Natural Thermal Unit. 



Any expression for the mechanical equivalent of heat which introduces 

 the degrees of a thermometer-scale, must have an arbitrary character which 

 may interfere with the ready conversion of thermal into other dynamic 

 measurements. Moreover, it may well be questioned whether the mass- 

 factor should be chosen, rather than the velocity-factor of vis viva, as a unit 

 of comparison. If we consider force as a representative of matter in mo- 

 tion, different kinds of force would seem to be fitly characterized by differ- 

 ences of velocity rather than by differences of mass. 



There is an obvious propriety in taking water as a representative medium, 

 but there is no more need of considering a pound, or a kilogram, or any 

 other definite ciuantity, in ordinary thermodynamic investigations, than 

 there is in chemical researches. The three changes of state through which 

 water passes, represent different well-defined amounts of work. The 

 changes from gas to vapor and from liquid to solid do not involve any 

 essential change of form, but the change from vapor to liquid converts an 

 indefinitely expansible and compressible substance into one which is but 

 slightly expansible and almost incompressible. It thus furnishes a natural 

 thermal unit (»^), which is a bond between tendencies to aggregation 

 and to dissociation and a convenient standard for comparison between the 

 equal actions and reactions of various forms of energy. 



An atom or quantity x of water, in passing from the fusing to the boil- 

 ing temperature, absorbs an energy sufficient to lift itself 772 X 180 feet, 

 or 423.54 X 100 metres. This represents a wave- or projectile-velocity 

 v^ = V2jh = 2986.3 feet = .56558 miles = .9102 kilometres per second. 



56. Weighing the Sun by the Thermometer. 



In two wave-systems, which are due, either directly or indirectly, to syn- 

 chronous actions and reactions betw^een two different masses, the wave- 

 velocities are proportioned to the producing masses ; for v^ oc gt oc -^ 

 oc fi. We have already found (Note 47) that the wave-velocity of solar 



*Proc. Amer. Phil. Soc, ix, 439. 



