Chemistry and Physics. 391 



" Now we have irrefragable dynamics proving that the whole 

 life of our sun as a luminary is a very moderate number of 

 million of years, probably less than 50 million, possibly between 

 50 and 100 million ! To be very liberal, let us give each of our 

 stars a life of a hundred million years as a luminary. Thus the 

 time taken hj light to travel from the outlying stars of our 

 sphere to the center would be about three and a quarter million 

 times the life of a star. Hence if all the stars through our vast 

 sphere commenced shining at the same time, three and a quarter 

 million times the life of a star would pass before the commence- 

 ment of light reaching the earth from the outlying stars, and at 

 no one instant would light be reaching the earth from more than 

 an excessively small proportion of all the stars. To make the 

 whole sky aglow with the light of all the stars at the same time 

 the commencement of the different stars must be timed earlier 

 and earlier for the more and more distant ones so that the time 

 of the arrival of the light of every one of these at the earth 

 may fall within the durations of the lights at the earth of all the 

 others." — Phil. Mag., August, 1901, pp. 161-177. J. t. 



11. Nineteenth Century Cloud over the Dynamical Theory of 

 Heat and .Light. — Lord Kelvin classifies these clouds as fol- 

 lows : Cloud I. Relative motion of ether and ponderable bodies. 

 Lord Kelvin discusses the various theories in regard to the con- 

 stitution of the ether, and in the course of this discussion remarks 

 upon the suggestion of Fitzgerald and of Lorenz, that the motion 

 of ether through matter may slightly alter its linear dimensions — 

 " according to which if the stone slab, constituting the sole plate 

 of Michelson and Morley's apparatus, had in virtue of its motion 

 through space occupied by the ether, its linear dimensions short- 

 ened one one-hundred-millionth in the direction of motion — the 

 result of the experiment would not disprove the free motion of 

 ether through space occupied by the earth." The author still 

 regards cloud I as very dense. Cloud II arises from a proposition 

 first enunciated by Waterston, which is as follows : 



" In mixed media the mean square molecular velocity is 

 inversely proportional to the specific weight of the molecule. 

 This is the law of the equilibrium of vis viva." Without any 

 knowledge of the paper of Waterston, Maxwell, in 1859, enunci- 

 ated the following proposition : "Two systems of particles move 

 in the same vessel : to prove that the mean vis viva of each parti- 

 cle will become the same in the two systems." This is also 

 Waterston's proposition regarding the law of partition of energy. 

 Lord Kelvin does not regard either the proof of Waterston or 

 that of Maxwell successful. The subsequent theorems of Boltz- 

 mann and Maxwell in regard to the equality of mean kinetic 

 energies, are also criticised. Lord Kelvin, after an exhaustive 

 criticism of the Boltzmann and Maxwell law, quotes Lord Ray- 

 leigh's remarks on the difficulties connected with the application 

 of the law of equal partition of energy to actual gases (Phil. 



Am. Jour. Scl— Fourth Series, Yol. XII, No. 71.— November, 1901. 



27 



