401 



and bacteria would produce this compouml, easily rocognisablo 

 by its colour. So, it' later it should l)e proved that the maiigaiiese 

 moulds really produce a substance causing oxidation out of the 

 cells, it may now already be asserted that it can neither be oxidase 

 nor chinon. 



BVom the preceding we see that with the oxidation of' mangano- 

 carbonate by microbes, many questions are related, worth a nearer 

 examination, especially with i-egard to the conversions which these 

 very common microbes cause in the soil. 



Physics. ^ ^'On the hiw of partition of energy.'' IV. By Prof. 

 J. D. VAN DER Waals Jk. (Communicated by Prof. J. D. van 



DER Waals.) 



§ 12. In my previous communications on this subject I started 

 from the earlier formula of Planck, in which no zero-point energy 

 was assumed. In fact the assumption of zero-point energv involves 

 great difficulties. In my opinion the supposition that a vibrator 

 vibrating with slighter energy than vli would not emit energy ^) is 

 not so much responsible for these difficulties — something similar 

 would already be found in a charge, which moved in a perfectly 

 conducting inclocure — but rather the assumption that radiation 

 coming from the outside yet acts on the electron in a normal way, 

 and sets it vibrating. '^) 



In spite of these difficulties Planck's later formula for the energy 

 of a vibrator has of late been preferred by different physicists. The 

 quantitative grounds adduced for this, seem to be still pretty un- 



1) Strictly speaking it might be said that Planck's vibrators in a certain sense 

 do radiate, also when they contain less energy than a quantum. For they absorb 

 energy, and absorption is a kind of emission. If e.g. we imagine a source of 

 light and a black screen and investigate the light behind the screen by means of 

 electro-magnetic potentials, we find darkness there, only because the contributions 

 to those potentials, yielded by the electrons of the screen, just cancel the contri- 

 butions • furnished by the electrons of the source of light. If the electrons of the 

 screen did not emit potentials and forces derived from them, we should have to 

 observe the direct light of the source behind the screen. So Planck's supposition 

 does not really come to this that vibrators when they do not possess exactly a 

 whole number of quanta, do not radiate, but that they radiate in a particular 

 way unilaterally. 



2) It is remarkable that it is assumed here that the elementary process of ab- 

 sorption is not reversible, whereas by the cooperation of many suchlike processes 

 reversible observable phenomena do originate. 



26 



Proceedings Royal Acad. Amsterdam. Vol. XVI. 



