6i6 SCIENCE PROGRESS 



of equilibrium, and calculates the number of such possible 

 vibrations from the elastic constants of the body. The quanta 

 being distributed among these degrees of freedom as above, 

 the formula for the heat energy can be calculated. 



On Planck's second theory, since the absorption of radiant 

 energy can take place continuously, and an atom cannot emit 

 less than an amount hv of energy, there must always remain 

 in the atom an amount of energy varying from O to h^, or 



a mean amount of energy — . This energy is the latent energy 



of the atom, which Wien ascribes to the energy of electrons in 

 the atom. He distinguishes between the electronic energy and 



the energy of the atom ; this mean amount — does not belong 



to the atomic energy considered by Debye in his treatment 

 of the specific heat problem, and so does not interfere with 

 the deduction of his formula. 



The theory of the electrical and thermal conductivities 

 presents still many problems which await solution. Drude's old 

 theory seems to be almost universally given up, since it stands 

 in contradiction to the radiation results, as demonstrated by 

 Lorentz, and also to the experiments on specific heats at low 

 temperatures. Lenard has worked out a theory based on the 

 assumption that the electrons in the metal are not gas-kinetically 

 reflected from the atoms, which seems impossible in the face 

 of recent experiment, but are absorbed by the atoms and sub- 

 sequently liberated, the liberation depending on the proximity 

 of the atoms (Nahewirkung). This gives the velocity of the 

 electron independent of the temperature, which is the assumption 

 favoured by Wien, who connects it with the latent energy 

 of the atoms mentioned above, which is independent of the 

 temperature. Many of the observed results are given by 

 Lenard's treatment ; it involves, however, in its present form 

 too many indeterminate factors to be very useful, and it is 

 doubtful if it will give the abnormally high conductivity of 

 metals at temperatures near the absolute zero found by Kammer- 

 lingh Onnes. Wien, using Debye's assumptions made for the 

 specific heat, has obtained a formula which gives a good agree- 

 ment with experiment in this direction, even for the very low 

 temperatures. But in both the electric and thermal conductivities 

 there are many points still unsatisfactorily explained, and, 



