TRANSACTIONS OF THE SECTIONS. &1 



On the Tliermo-Dynamics of the General Oceanic Circulation. 

 By William B. Caepentee, LL.D., M.D., F.B.S. 



The object of this communication was to bring under the consideration of Phy- 

 sicists the fa.ct, ascertained by recent Deep-Sea explorations, of the general preva- 

 lence of a temperature not much above 32° F. over the bottom of the great Ocean- 

 beds, at depths greater than 2000 fethoms. As it has been proved by Temperature- 

 soundings made in the Mediterranean that the temperature of its bottom at like 

 depths is about 54° F., it is obvious that depth, per se, has no relation to the pheno- 

 menon. And the explanation of it propounded by the author is, (1) that a body of 

 Polar water flows over the deepest portions of the Oceanic basins which commimi- 

 cate with the Arctic and Antarctic areas ; (2) that this flow has its origin in the 

 action of Polar cold on the water subjected to its influence, whereby a descending 

 movement is imparted to the whole mass ; besides which, the Polar colimm, in 

 virtue of its greater density, will have a gi-eater downward pressure than the 

 Equatorial column at the same level ; (3) that this bottom outflow will produce 

 an indraught of the more superficial stratum of Ocean water towards the Polar 

 areas ; (4) and that a vertical circidaiion will thus be maintained by dift'ereuce of 

 Temperature alone, canying the lower cold stratum of Ocean water h-om the Polar 

 towards the Equatorial area, and the upper warm stratum from the Equatorial to- 

 wards the Polar. 



A diflerent explanation of the facts, however, has been oifered by those who 

 regard the Horizoniul Circulation, of which the Trade-winds are the jn-imum 

 mobile, as the sole cause of the amelioration of the temperature of the Arctic basin, 

 by an afiiux of warm water ; for it has been urged that the driving ofl" of the 

 superficial stratum of Equatorial water in the Gulf-stream must produce a partial 

 void in that area, which will be filled by a deep indraught of Polar water. — This 

 appears to the author extremely improbable, on general physical gTOunds. A 

 horizontal movement of surface-water in the open Ocean would not draw up water 

 from below, so long as a lateral influx can keep up its level ; so that any such 

 horizontal Wind-current must have another horizontal movement to complete the 

 circulation. Such a horizontal complement is obvious in the case of the Gulf- 

 stream, of which one portion turns round the Azores to re-enter the Equatorial 

 current, thus completing the shorter circulation ; whilst the other portion, which 

 flows onwards in a N.E. direction, has as its complement the various cold 

 surface-cm-rents which are known to set southwards, and of wliicli it is shown by 

 recent observations that one tends towards the coast of Mogador, sending an ofiset 

 through the Strait of Gibraltar. 



Further, it was argued by the author that the temperature-phenomena obtained 

 in recent explorations indicate tliat a N.E. movement of the upper stratum of 

 Oceanic water extends between the coast of Spain and the Faroe Islands to a depth 

 of 500 or 600 fathoms, and that while this cannot be attributed to any propulsive 

 action derived from the Gulf-stream (the thinned out edge of which is less than 50 

 fathoms in depth), it is exactly such a flow as wo\ild be anticipated on the hypo- 

 thesis of a vertical circulation sustained by opposition of Temperature. 



0*1 tlie Mathematical Theory of Atmospheric Tides. 

 By the Rev. Professor Challis, M.A., LL.D., F.B.S. 



The purpose of the author in this communication was to point out a process of 

 analytical reasoning by which the solution of the problem of atmospheric tides 

 might be strictly derived from the general equations of hydrodynamics. For the 

 sake of simplicity, the surface on which the atmosphere rests was supposed to be 

 exactly spherical, the earth was conceived to have no motion of rotation, and the 

 tidal motion to be produced by the moon revolving westward in the plane of the 

 earth's equator, at her mean distance (R), and with the mean relative angular 

 velocity (/x). Also it was assumed that the relation between the pressure (p) and 

 density (p) is at all times and at all points of the atmosphere j9=ff-p, the eftects of 

 variation of temperature not being taken into account. 



As tidal motion is oscillatory, and the oscillations are so small that it is uu- 



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