MODELS OF POSITIVE ION 311 



gradually, as the aix is rarefied, into the volume 

 of the gas. It also occurs only at pressures about 

 which the other phenomena of phosphorescence in 

 gases take place, the limits, however, being some- 

 what wider. 



If the thickness of the layer is comparable with 

 the sphere of molecular forces, the amount of 

 chemical decomposition will also be very small, 

 as the quantity of matter will be equally so. 

 R. Threlfall and Miss Martin {Proc. Comb. Phil. 

 Soc, 1877) endeavoured to detect the presence of 

 ozone at the pressures at which a variation from 

 Boyle's law had been found to exist by Bohr, Baly 

 and Eamsay, and others, but they failed to detect 

 any traces of it by chemical means. 



The chemical changes which take place at the 

 surface layers, which we have been considering, 

 may be such as we have no experience of at the 

 ordinary temperature from experiments with large 

 masses. 



Chemical Combinations in High Vacua 



We have put forward the hypothesis, which, as 

 we have seen, has found support in the results 

 of numerous experiments described in this and in 

 previous works, and also in those by various other 

 investigators, that the phosphorescence in gases is 

 started by the interchange of carriers between atoms 

 that do not carry the charges that correspond to them, 

 such, for instance, as a positively charged oxygen 



