May 1 8th, 1920.] Proceedings. xxvii. 



These results show that the alumina growths formed by the 

 presence of mercury on aluminium appeared to carry with them 

 mechanically a quantity of mercury depending on the amount 

 present in excess upon the surface ; and that they do not form 

 at all unless such excess exists on the surface. 



With a moderate excess the growth is pure white, with a 

 large excess it appears grey and the quantity of mercury 

 associated with the alumina formed depends on the excess 

 present. 



The method of growth appears to be somewhat erratic but 

 in several cases quite interesting. In one experiment we made 

 by incorporating the amalgamated wire with a drop of mercury 

 which had afterwards a perfectly smooth surface, a growth 

 appeared over the whole of the top surface and none on the 

 sides ; this growth increased but gradually ceased around the 

 periphery, the central growth continuing till it appeared as a 

 truly-formed inverted cone supported on its apex on the drop 

 of mercury. 



On repeating this experiment several times the growths 

 appeared as a profusion of filaments completely covering the 

 globule of mercury and extending for half an inch around it. 



Neither pure damp oxygen nor ozone had any effect in 

 accelerating or adding to the profusion of the growths. 



The study of the action of mercury on aluminium is 

 extremely interesting as regards the character of this metal ; 

 if aluminium be put in water no action is observed, but when 

 amalgamated it immediately decomposes the water liberating 

 hydrogen ; when zinc is amalgamated, the mercury tends to 

 resist the action of the water on the zinc and this is still more 

 marked when the amalgamated zinc is immersed in weak acid. 

 Under these conditions it resists the action of the acid but if 

 immersed in its unamalgamated condition the weak acid attacks 

 it at once. ^ 



Professor Sydney Chapman, M.A., D.Sc, F.R.S., made a 

 few remarks on "The Lunar Tide in the Earth's 

 Atmosphere," in which he pointed out that the atmosphere, 

 like the oceans and the solid earth, is subject to the tidal 

 influences of the sun and the moon. The barometric pressure 

 shows a very minute tidal variation with the period of half a 

 lunar day, this variation being determined only b}^ a difficult 

 process of averaging-out other regular and irregular variations 

 from long series of hourly barometric observations, so that data 

 from very few stations are available. Many questions sug- 

 gested by the data remain unanswered, but as further data 

 become available, and the theory of atmospheric tides is 

 extended, our knowledge of our atmosphere may become of 

 very great importance. 



