There are some questions, seemingly innocent enough, which yet appear fated to rouse to unusual warmth all who take part in their discussion. One cannot, for instance, find anything obviously tending to warmth of temper in the telescopic study of a planet; yet the elder Cassini was moved to passionate invective by certain observations of Mars not perfectly according with his own; and Sir W. Herschel, usually so philosophic, was roused by Schroter's recognition of mountains in Venus to deliver himself of a criticism justly described by Arago as 'fort vive, et, en apparence du moins, quelque peu passionnee.' The question, again, whether the 'Eozoon Canadense' is a true 'Rhizopod,' though not altogether removed from the region of hard words, might appear to be unlikely to excite warlike emotions; yet there has been some very pretty fighting over it. The solar corona has in like manner given occasion for rather strong writing; and if, on the one hand, the supporters of a lately-abandoned theory said of their opponents that 'they made themselves ridiculous,' these, in their turn, at times used a tone reminding one of the scholar who said of a rival, 'May God confound him for his theory of the Irregular Verbs:' yet the corona seems at a first view rather calculated to produce a sedative effect than to excite unphilosophic wrath. The subject of oceanic circulation would appear to belong to the class of questions here considered.

The very name of the Gulf Stream is to some physical geographers as a red cloth is to a bull. Even Sir John Herschel, usually placidity itself, was moved when he spoke on this point. But though he and Maury grew warm enough in its discussion, their warmth was ice-cold compared with the fire of more recent disputants. We have before us the latest contribution to the subject, a rather ponderous essay in one of our leading quarterlies; and herein we find pleasing references to the 'stupidities' of one set of opponents, the 'shallow nonsense' of a second, 'the wrong-headedness' of a third, with other similar amenities. More than once during the progress of this controversy the gentle public has been reminded of Bret Harte's remarks about the row That broke up the Society upon the Stanislow; and has been inclined to urge, with ' Truthful James,' that they

Hold it is not decent for a scientific gent To say another is an ass,-at least to all intent; Nor should the individual who happens to be meant, Reply by heaving rocks at him to any great extent.

The controversy has not, indeed, reached this last stage of development, and we trust it never will; but it has gone so near to it as to suggest that the disputants have wished to demonstrate, by example, the justice of Darwin's theory about the human 'snarling muscles.'!

I propose to inquire into the subject which has been thus warmly discussed, trusting not to be myself inveigled by it into any warmth of expression. Indeed, but for the fate of others, I should feel no anxiety on this point, though I have myself a favourite theory to uphold respecting one branch of the subject. As it is, I share something of the feeling of the Red Cross Knight when he was approaching 'Foul Error's den,' and his monitress said to him, ' The perils of this place I better wot than thou; therefore I rede, Beware.' I am not without hope, however, that I may be able to keep my snarling muscles quiescent.

1 ' He who rejects with scorn the belief that the shape of his own canine teeth, and their occasional great development in other men, are due to our early progenitors having been provided with these formidable weapons, will probably reveal, by sneering, the line of his own descent. For though he no longer intends, nor has the power, to use these teeth as weapons, he will unconsciously retract his "snarling muscles " (thus named by Sir Charles Bell), so as to expose them ready for action, like a dog prepared to fight.'-Darwin's 'Descent of Man,' vol. i. p. 176. "We may mention, by the way, that an instance has recently occurred, in which the human teeth were used to some purpose against one of the recognised masters in the art of biting. A man, proceeding in company with several others through a wood, was attacked by a hyena (usually one of the most cowardly of beasts). His companions fled, and having no weapon he was reduced to the necessity of showing tooth for tooth, and taking a good grip of the hyena's nose, he compelled that gentleman to howl with anguish. On this, the man's companions returned and presently beat the hyena to death.

I shall direct attention chiefly to the Atlantic currents, as being those whose real direction and extent are best known, and those, moreover, whose characteristics are most important to European nations.

Let us begin with the surface currents, and though the system of surface circulation can scarcely be said to have a real beginning, let us start with the great equatorial currents which flow westwards from the Gulf of Guinea,1 or more correctly from the Bight of Biafra. We speak of the westwardly equatorial currents, because not unfrequently there is an equatorial eastward current running between two much more important tropical westward currents. Yet ordinarily there is one great westward current running in an unbroken stream from equatorial Africa to the shores of Brazil, and even when this great current is divided into two by an eastward current this last is only to be regarded as a sort of 'backwater.' The water moving westwards is relatively cold, more especially on the African side of the Atlantic.

1 Along the shores of the Gulf of Guinea there flows an easterly current, several degrees warmer than the equatorial current.

The accompanying map exhibits the nature of the surface circulation of the North Atlantic. It is constructed on one of the forms of equal-surface projection described in my 'Essays on Astronomy,' and has the advantage over the ordinary Mercator's charts of exhibiting the true dimensions of the various currents. I would, however, invite the student who wishes to familiarise himself with the true nature of the Atlantic currents to construct other maps; for instance, a polar map on the first method of equal-surface projection described in that essay (see pp. 264, 265), and a map of the whole Atlantic on the second plan, taking the meridian 40° west of Greenwich as the central one.