June 22, 1900.] 



SCIENCE. 



985 



"Its discovere.r, J. CI. Maxwell, first proved 

 it by the assumption of a principle which, 

 though true, itself needs proof. Since Maxwell 

 himself recognized this defect, he later gave a 

 second proof, the basis of which is subject to no 

 doubt " (p. 45). " L. Boltzmann completed and 

 perfected this proof by employing stricter 

 mathematical work, and thus removing just 

 ground for doubt. A further step forward 

 [1887] we owe to H. A. Lorentz, who raised a 

 new objection and improved the calculation, 

 thereby inciting Boltzmann to again give a new 

 proof [1887], which proof may now be con- 

 sidered as quite free from objection. 



" Further, Kirchhoflf has given a proof of the 

 law in his Lectures [1894] ; but against this, 

 too, according to a remark of Boltzmann, ob- 

 jection may be made. 



" In a different way the proof of this law was 

 attempted in the first edition of this book. The 

 weak points of this attempt were removed by 

 N. N. Pirogoff [1885], and a varied form of 

 PirogofF's proof is given in the second of the 

 Mathematical Appendices [of this book] " (p. 

 46.) 



§ 34, on pressure of a gas in motion, and 

 g 35, on reaction and cross-pressure, contain 

 matter especially referred to in the preface 

 as not in the first edition. They have per- 

 haps nothing more quotable than the last para- 

 graph of § 35, which is notable as including the 

 only mis-translation that I have observed in the 

 English edition. The paragraph reads, "Since 

 these formulae contains the velocity only in its 

 square, they are independent of the direction of 

 the motion, andhold, therefore, as well for io-and- 

 fro oscillations as for propagation of the longitudi- 

 nal waves of sound. On this depend the apparent 

 attractions and repulsions in air when sounding 

 and in the ribbed dust-figures of Kundt." The 

 German of the lines which I have underscored 

 is, " gelten also auch fur hin und her gehende 

 Schivingungen, wis sie bei der Fortpflanzung der 

 longitudinalen Schallwellen auftreten V ' 



From § 38, on thermal effusion, "Just as 

 effusion results from a difference of pressure at 

 the two sides of a porous partition, so can a 

 similar phenomenon be brought about by a dif- 

 ference of temperature of the two sides of a par- 

 tition ; and the latter phenomenon, according 



to Maxwell's suggestion, is called thermal effu- 

 sion. 



"The possibility of in this way producing a 

 flow of gas by means of an unequal distribution 

 of temperature, was first pointed out by Carl 

 Neumann when he was attempting to explain 

 the production of a thermo-electric current by 

 analogy with a thermal diffusion." 



Chapter IV. — Ideal and Actual Oases. 



' 'From numerous observations which Galitzine 

 has partly made by himself and partly drawn 

 from other sources, the pressure of a mixture 

 [of gases] is sometimes greater and sometimes 

 less than the sum of the pressures exerted 

 by the components separately" (p. 92). §47 

 deals very briefly with attempts to improve 

 upon the formula of van der Waals's. 



Chapter V. — Molecular and Atomic Energy. 



"That monatomic gaseous molecules also may 

 be capable of oscillatory motions in their inte- 

 rior we may look upon as probable, since in 

 their spectra whole series of different lines are 

 found. But these motions, as we may assume 

 in accordance with E. Wiedemann's observa- 

 tions, require so small an expenditure of energy 

 that its amount does not come at all into account 

 in comparison with the kinetic energy of the 

 molecular motion. 



" Hence monatomic molecules need in no 

 way be rigid massive points ; ic is only neces- 

 sary that they should be very small particles in 

 whose interior only such motions can come into 

 play as demand but very little energy. It 

 therefore does not appear impossible that the 

 ratio C ^ c =: 1.67 should be found in the case 

 of chemically compound molecules also, if the 

 connection of the atoms is so firm that internal 

 motions are excluded " (p. 121). 



The last quotation brings us near a very 

 active crater of debate, the eruptions of which 

 have been familiar to readers of English scien- 

 tific periodicals for years ; namely, the question 

 of equal distribution of energy among the dif- 

 ferent degrees of freedom of a system. Into 

 the general question Meyer does not go, but 

 insists, as in his first edition, that, with such 

 limited freedom as the atoms have within the 

 molecule, the law of uniform distribution of 

 energy among the various degrees of freedom 



