FORMATION OF AGGREGATES 271 



is to increase the number of molecules that cluster 

 round it, and therefore the size of the group. The 

 ion tends to become larger and larger unless there 

 is some counteracting process at work to check 

 its growth. Now the surface-tension would tend 

 to do this, so that the maximum size of the aggre- 

 gate is that which would be obtained when equi- 

 librium is arrived at between the contending 

 forces. 



A stage would thus be reached at which the 

 presence of ions will overpower that of surface- 

 tension. 



The electrification which promotes condensation is 

 bound at a certain point to overpower the surface- 

 tension which tends to prevent this, at any rate 

 for very small drops, because the effect due to 

 surface-tension varies inversely as the radius of 

 curvature, whilst that due to electrification varies 

 inversely as the square of the radius of curvature. 

 Hence, when the surface-tension is destroyed the 

 aggregates of molecules will fly to bits by the dis- 

 integration of the constituent parts, the luminosity 

 being a consequence of the energy thus radiated. 



The ratio of the energy given out by a molecule 

 or particle, or group of molecules of molecular 

 dimension, by condensation, to the potential energy 

 varies directly as the radius of curvature, so that 

 more energy will be given out by the negative 

 ions on which its condensation takes place than 

 by the positive ones, as the condensation on these 

 is much larger. 



