1893.] on Fog, Clouds and Lightning. 107 



and gradually relapses into ordinary oxygen, the process being that 

 one atom is dropped from the three-atom molecules of ozone, these 

 detached atoms in course of time uniting with one another to form 

 pairs. Thus two molecules of ozone are transformed into three of 

 oxygen. A body of ozone is therefore always attended by a number 

 of dissociated atoms which are looking for partners. 



In the steam jet experiment there is not time for the dis- 

 engagement of a sufficient number of isolated atoms from a blast of 

 ozone to produce any sensible effect. But the case is otherwise when 

 the vapour is confined in a closed vessel, as in Mascart's experiment, 

 or when it occurs in the clouds, where the movement of air and vapour 

 is comparatively slow. 



Ozone, it will be remembered, was found by Mascart to produce 

 dense condensation in a closed vessel even after being filtered through 

 cotton wool. Similar filtration seems to entirely deprive the so- 

 called products of combustion of their active property, a fact which 

 has been adduced as affording overwhelming evidence in favour of 

 the dust nucleus theory. Coulier himself, however, detected a weak 

 point in this argument. He produced a flame which could not 

 possibly have contained any products of combustion except steam, 

 by burning pure filtered hydrogen in filtered air ; yet this product 

 was found to be perfectly capable of causing dense condensation, and, 

 as in his former experiments, filtration through cotton wool deprived 

 it of its activity. 



These anomalies may, I think, be to a great extent cleared up if 

 we assume that the effect of the cotton wool depends, not upon the 

 mere mechanical obstruction it offers to the passage of particles of 

 matter, but upon the moisture which it certainly contains, and which 

 may act by attracting and facilitating the reunion of dissociated 

 atoms before they reach the air inside the vessel. According to this 

 view ozone would remain an active condenser in spite of its fil- 

 tration, because free atoms would continue to be given off by it after 

 it had passed the cotton wool. The filtration experiment should be 

 tried with perfectly dry cotton wool, which, however, will not be 

 easily procured, and if my suggestion is right, dry wool will be 

 found not to deprive ordinary products of combustion of their con- 

 densing power. 



To sum up. I think my recent experiments show conclusively 

 that the dense condensation of the steam jet is not due directly either 

 to electrical action or to dust nuclei. The immediate cause is pro- 

 bably to be found in dissociated atoms of atmospheric gases, though 

 as to how these act we can only form a vague guess. 



The discourse concluded with some remarks upon atmospheric 

 electricity, and the exhibition of lantern photographs of lightning 

 flashes. 



[S.B.J 



