293 On the Pmctical'd'Uy 



some communication ; yet surely it does not anthoiizs us to pre- 

 sume that there is "an uninterrupted communication." On the 

 contrary, it seems probable, that there may be islands or shoals 

 between the north-west coast of Greenland and the north-east 

 coast of Auierica, among which smaller masses of ice, trees, and 

 whales too, as well as the current, may find a passage down 

 Davis's Strait from the polar basin ; but which maybe, and pro- 

 bably are, so blocked up generally by mountains and large fields 

 of ice, as to present an impassable barrier for ships. 



On account of the current, it is certainly fair to presume, that 

 the northern part of Davis's Strait is misnamed in the charts as 

 *' a bay ;" for if it were one, it certainly " would be very difficult 

 to explain, how a current that runs to the southward perpetually, 

 with a velocity of four and sometimes oijive miles an hour, could 

 originate in the bottom of it ! " 7/" there is an miinterrupted com- 

 munication, that is, if there is no land, no shoals in the whole 

 space between Greenland and America, it appears very probable 

 that greater quantities of ice would pass through that space with 

 a current of such velocihj ; and less find its way round Green- 

 land. But we must endeavour, first, to decide in our own mindsj 

 as well as we can, how and where the ice in the polar regions is 

 formed. In what direction it is probably impelled by the winds 

 and currents. How these winds probably prevail in summer, and 

 winter, and how the current probably sets underneath, as well as 

 at the surface of the water. For, notwithstanding the writer of 

 the article I am examining, apprehends it will be " found, that 

 the currents of the ocean, where no land intervenes, are entirely 

 superficial ;" and though he says, " it would be difficult to ex- 

 plain the perpetual egress of a current, from the polar basin into 

 the Atlantic, without admitting a supply through the only re- 

 maining opening (Behring's Strait,) into that basin, to answer 

 the demand of the current," I yet firmly believe there must be a 

 continual u?idcr flow of water in the ocean, as well as superficial 

 currents. Otherwise, that "universal motion of the great deep," 

 which he, and all must allow, cannot l)e satisfactorily accounted 

 for. How then, it may be asked, are these lower currents to be 

 accounted for? The question is much easier to be put, than solved 

 to the satisfaction of others. But I will endeavour to explain 

 the ideas I have on the subject as well as I can ; and that, too, 

 with all the diffidence of one who knows that, though conjectures 

 may, perhaps, be well-founded, their truth depends on experi- 

 ment. 



The conjectures I venture to oflFcr, are founded, however, on 

 the known and acknowledged properties of heat and cold. Heat 

 is known to be the general cause of the expansion of air, and cold 

 the cause of its com.pression. Heat rarefies, and cold condenses. 



The 



