330 RECORD OF SCIENCE FOR 1886. 



in order to be able to subordinate it to all reversible processes, the 

 si)eakerliad uudertakeu sometrausforinations of it, and had introduced 

 into it the conception of the " kinetic potential." In the form it has 

 thus attained, the Hamiltonian law — the old principle of the actio 

 minima — has iu point of fact universal validity. It has just as wide an 

 applicatiou as has the law of the conservation of energy and reveals a 

 whole series of mutual relations between the different physical proc- 

 esses. (Nature, July, 1886, xxxiv, 308.) 



Becker has propounded a theorem of maximum dissipativity, as fol- 

 lows : In all moving systems there^s a constant tendency to motions 

 of shorter period. And moreover if there is a sufficient ditference be- 

 tween the periods compared, this tendency is always a maximum, so 

 that all natural phenomena occur in such a way as to convert the 

 greatest possible quantity of the energy of sensible motion into heat, or 

 the greatest possible quantity of heat into light, etc., in a given time, 

 provided that the interval of time considered exceeds a certain frac- 

 tion of the period of the most rapidly moving particles of the system. 

 From this it follows immediately that the higher forms of energy can be 

 produced from the lower, or motions of longer period from those of 

 shorter period, oul^' on condition that the sum of the transformations of 

 the system is equivalent to a degradation ; a result nearly identical 

 with one of the chief deductions from the second law of thermodynamics. 

 (Am. J. Sci., February, 188G, III, xxxi, 115.) 



Tait has undertaken a mathematical investigation upon the ])artition 

 of energy between two systems of colliding spheres, because since 1800, 

 when Clerk Maxwell published his first grand investigation on the sub- 

 ject, it seems to have been taken for granted than in a mixture of great 

 numbers of colliding spherical particles of two kinds, the ultimate state 

 would be one in which the average energy of translation is the same 

 for a sphere of either kind. (Nature, January, 1886, xxxiii, 270.) 



Exuer has employed a new method for calculating the size of mole- 

 cules. The Kinetic theory of gases gives the diameter of a molecule 

 as a fraction of the mean length of free path and of the ratio of the 

 space actuallj" occupied by the material liarticles to their api)arent 

 volume. Clausius has obtained this latter value iu terms of the dielec- 

 tric constant; and since this is equal to the square of the refractive 

 index, in terms also of this index. Hence, knowing the mean length of 

 free path of the molecules of any gas (determined from diffusion or in- 

 terior friction) and its index of refraction, the actual diameter of the 

 molecules may be calculated. Exner's figures are as follows, expressed 

 in centimeters. They should all be multiplied by 10^ : Air 10, CO2 13, 

 CO 13, H3 10, CH4 12, C2 H4 21, NH3 16, H2 O 19, N 17, NO 16, O, 16, 

 H2 S 22, HCe 18, SO2 17, Ccz 19, and C2 N2 19. To. this table the 

 author has added the relative atomic volumes and relative specific 

 weights of certain substances. By the latter is to be understood the 

 weight in grams of one cubic centimeter filled with the molecules on 



