142 Mr. G. Gore on the Adhesion 



sphere a few feet above it, were decidedly less considerable than 

 what had been ascertained by M. Martens and myself to be the 

 case in France and Switzerland under similar circumstances. I 

 was, at the time I received this communication, totally unaware 

 of the still more striking differences my son has since found to 

 exist in Queensland. 



It may perhaps be alleged that the explanation I have ven- 

 tured to offer can hardly be reconciled with the striking and often 

 dangerous contrast travellers in the great African deserts have 

 observed between the oppressive heat of the day and the sudden 

 cold which occurs immediately after sunset. The objection, I 

 think, may be answered as follows: — In the vast deserts of 

 Africa, the almost complete absence of water of any kind tends 

 to maintain the atmosphere in a state of comparative absolute dry- 

 ness ; for although it is true that the quantity of aqueous vapour 

 the atmosphere can take up depends mainly on its temperature, 

 still water must be present; and if there be none, or hardly any, 

 the air, however warm, can no longer take up a sufficient quan- 

 tity of vapour to intercept any considerable proportion of the 

 heat radiated by the earth. Under these circumstances, there is 

 no longer any reason why the cold arising from nocturnal radia- 

 tion should not attain its maximum, producing a striking and 

 sometimes dangerous contrast in the temperature of the sur- 

 rounding atmosphere the moment the sun disappears beneath 

 the horizon. 



XVIII. Experiments on the Adhesion of Liquids to Mercury. 

 By G. Gore, Esq.* 



IF a drop of Nordhausen sulphuric acid, about one-tenth of an 

 inch in diameter, is carefully placed by means of a glass rod 

 upon the centre of a clean globule of pure mercury about 80 

 grains in weight, it instantly diffuses itself in a thin film over 

 the surface of the metal, and the mercury becomes flattened and 

 exhibits vortical movements all over its surface : but if the expe- 

 riment is made with a strong aqueous solution of ammonia or of 

 caustic potash, no such results occur; the alkaline solution con- 

 tracts itself into a spherical form and persistently floats to the 

 side of the mercury without spreading itself over the surface, 

 especially if the mercurial globule weighs less than 60 grains. 



To ascertain the order in which various liquids stood with 

 regard to this particular behaviour with mercury, a number of 

 experiments were made. Pure mercury, contained in a clean 



* Communicated by the Author. 



