TRANSACTIONS OP THE SECTIONS. 43 



usual rule — an <M*<warcl movement being found in the deepest stratum, while the 

 middle stratum was moving inwards, though the water of both these strata had the 

 lensity of the ^Egean. These anomalies are considered by Capt. Wharton to pro- 

 ceed from the prevalence of opposite winds at the two ends of the Strait. 



As a general rule, the strength of the wward undercurrent was proportioned 

 to that of the o«<<ward surface-current ; and this was very remarkably shown in 

 cases in which, both having been slack during a calm, an increase of wind aug- 

 mented the rates of both cuiTents alike. That a vdnd blowing o«<iwards should 

 promote the flow of an undercm-rent wjwards, may at first sight appear anomalous ; 

 but it is veiy easily accounted for. Suppose that a moderate S.W. wind, by 

 checking the surface-outflow, keeps the level of the Black Sea just so much above 

 that of the ^gean that the greater iceicjht of the latter column is counterpoised 

 by the greater height of the former ; then, as the hottoin pressures of the two are 

 equal, their lateral pressures will also be equal, and there will be no undercurrent 

 so long as this condition lasts. But so soon as, on the cessation of the S.W. 

 wind, the level of the Black Sea is lowered by a surface-outflow, the ^gean 

 column comes to be the heavier, and its excess of lateral pressure produces a deep 

 inflow. And when this out^o-w is further aided by a N.E. wind, so that the levels 

 of the two seas are equalized, or there is even an excess of elevation at the yEgean 

 end, the greater weight of the vEgean column will produce a greater lateral pres- 

 sure, and will consequently increase the force of the i/(ward undercurrent. 



The result of this experimentum crucis may be fairly considered to have clearly 

 shown that a slight excess of dowmvard pressure — whether arising from difference 

 of specific gravity, or from difference of level — is quite adequate to produce move- 

 ment in great bodies of water, which movement may have the rate and force of a 

 cwrent when restricted to a narrow channel. And the " creeping-flow " of Polar 

 water along the Ocean-bottom, which, on Dr. Carpenter's theory of Oceanic 

 circulation, brings a glacial temperature into the Intertropical zone, is thus found 

 to have an adequate vera causa in the excess of deep lateral pressure exerted by the 

 Polar column, whose density has been augmented by cold, over that of the Equa- 

 torial column, whose density has been diminished by heat, — the levels of the two 

 columns being assumed to be the same. 



On the Refi'action of Liquid Waves. By W. S. Davis. 



Lunar Influence on Cflouds and Rain. Btj J. Park Hakeison, M.A. 



On tabulating the mean quantities of cloud at Greenwich in 1871 according to 

 the age of the moon, the results agreed generally with the mean rainfall on certain 

 days of the lunation as ascertained by Mr. Chase, an American savant, and Mr. 

 Hennessj', at Mussoorie, in India. The author pointed out the necessity of obtain- 

 ing special observations, not only of the amount of cloud, but also its height above 

 the earth, before any certain conclusions as to the fuU extent of lunar influence on 

 the atmosphere, and consequently on air-temperature, can be arrived at. He had 

 shown in former communications that temperature is sensibly afiected by the moon. 



On the Application of Teler/raphy to Navigation and Meteorology. 

 By AsTURO DE Maecoarttj. 



On a Periodicity of Cyclones and Rainfall in connexion with the Sun-spot 

 Periodicity. By C. Melbrum. 



[Ordered to be prmted in extenso among the Eeports.] 



