150 Scientific Proceedings, Royal Dublin Society. 



surface to the bottom of a mass of water, must be of much greater importance 

 than diffusion, which is such an extremely slow process that months are 

 required to detect its action even in the laboratory. This is further indicated 

 by the fact that, to examine the effects of true difiusion experimentally, it 

 would be necessary to take great care to maintain an absolutely uniform 

 temperature, and to protect the column of water under observation from 

 any external agency which might result in producing currents in the 

 water. 



The experiments so far discussed have been made with very shallow 

 depths of water not more than about 260 mm. from the surface. It is, of 

 course, necessary to extend them in order to investigate the question as to what 

 depths mixing is appreciably induced by the conditions brought about by the 

 evaporation from the exposed surfaces of quiescent waters, fresh or salt, under 

 laboratory conditions. But such experiments would require observations to 

 be carried on for very long periods of time, and very great care would be 

 necessary to ensure uniformity in the conditions affecting evaporation during 

 their continuance. The authors have not hitherto had time or opportunity of 

 carrying out such experiments, but it is hoped to commence some experiments 

 of this kind in this College next session. 



A number of preliminary experiments have been made by one of the 

 authors with columns of water of from 18 to 24 mm. cross-section,^ and of 

 such length to allow of observations to be made to depths of about 1800 mm. 

 The results of these experiments prove that mixing induced by evaporation 

 from the exposed surfaces of columns of water does take place down to depths 

 of at least 1800 mm., and that it occurs to a more decided extent in sea than 

 in fresh water. Each of these experiments, however, extended over a 

 considerable number of days, and no precautious were made to keep the 

 conditions of evaporation from the exposed surfaces of the columns of water 

 \iniform. The results that were obtained from different experiments were 

 consequently not sufficiently concurrent to determine whether they could be 

 brought within the simple law found for the more shallow depths of water or 

 not. 



The following experiment goes to show that the concentrated layers of 

 salt solution, which result from evaporation at the exposed surface of a 

 de-aerated column of sea-water, stream downwards, as they are formed, with 

 little or no tendency to dissipation of their dissolved air-content in lateral 

 directions. 



'See "Unrecognized Factors in the Transmission of Gases through Water." By 

 W, E. Adeney, Phil. Mag., March, 1905. 



