Imágenes de páginas

am now inquiring) has no agreement with the monthly; nor again is the flow of the sea found to follow any of the conditions of the moon. For whether the moon be in her increase or wane, whether under the earth or above it, whether elevated high or low above the horizon, or whether situated in the meridian or elsewhere, in none of these instances has the ebb and flow of the sea any correspondence.

Therefore dismissing the moon let us inquire of other correspondences. Now of all celestial motions the diurnal is plainly the shortest, and accomplished in the least time (namely, in the space of twenty-four hours). It is natural therefore to refer this motion whereof we are inquiring (which is still shorter than the diurnal motion by three fourths) to that motion among the celestial bodies which is shortest; but this does not press the matter. What weighs more with me, is that this motion is so distributed as to correspond to the divisions of the diurnal motion; so that although the motion of the waters is almost infinitely slower than the diurnal motion, it is yet commensurable with it. For six hours is a quarter of the diurnal motion, and six hours is (as I have said) the time of this motion of the sea, with a difference coinciding with the measure of the moon's motion. Of this therefore I am fully persuaded, and take it almost for an oracle, that this motion is of the same kind as the diurnal motion. Taking therefore this as a foundation, I shall proceed to inquire of the rest; and I judge that the whole matter may be resolved by three inquiries. First, does this diurnal motion confine itself to the limits of the heaven, or does it descend and reach lower bodies? Secondly, do the seas move regularly from east to west as the heavens do? Thirdly, whence and in what manner proceeds the reciprocation of the tides every six hours, coinciding with a fourth part of the diurnal motion, though with a difference coinciding with the motion of the moon? With regard to the first inquiry, I judge that the motion of rotation or conversion from east to west is not properly a celestial but quite a cosmical motion; a motion primarily belonging to the great fluids, and found from the summits of heaven to the depths of the water; the inclination being always the same, though the degrees of velocity vary greatly; varying, however, in a regular order, so that the swiftness of the motion diminishes the nearer the bodies approach the earth. Now in the first place that this motion is not termi

[blocks in formation]

nated with the heaven, may be probably inferred from the fact that it prevails in full vigour through such an immense depth of heaven as that which lies between the starry heaven and the moon (a space much larger than that between the moon and the earth), decreasing regularly all the way; whence it is not likely that nature should throw off suddenly and at once a correspondence of this kind, which has been continued with a gradual abatement for such an immense distance. That this is the case in celestial bodies is proved by two inconveniences which would otherwise follow. For as it is manifest to the sense that the planets perform a diurnal motion, we must necessarily, unless this motion be set down as natural and proper to all planets, take refuge either in the violence of the primum mobile, which is directly contrary to nature, or in the rotation of the earth, -a supposition arbitrary enough, as far as physical reasons are concerned. In the heavens therefore the thing is so. And leaving the heavens, this motion is further seen most plainly in the lower comets, which, though they are lower than the moon, yet evidently revolve from east to west. For though they have their own solitary and irregular motions, yet in the performance thereof they still participate in the motion of the ether, and move in the same direction. They do not commonly keep within the tropics, and have no regular spirals, but run out sometimes towards the poles; but nevertheless they revolve in order from east to west. And this motion of theirs, though greatly diminished (since the nearer they approach to the earth the smaller are the circles in which they revolve, and the slower is the motion), still remains vigorous, so that it can overcome great distances in a short time. For these comets move round the whole circumference both of the earth and the lower air in the space of about four and twenty hours, with one or two hours over. But when descending gradually we come to those regions on which the earth acts not only by a communication of its nature and virtue (which checks and quiets the circular motion), but likewise by a material infusion of the particles of its substance in thick vapours and exhalations, this motion is immensely deadened and almost collapses; and yet it is not thereby completely exhausted and stopped, but remains in a languid and as it were latent state. For it is now acknowledged that in sailing within the tropics, where from the openness of the sea the motion of the air is best perceived,

and where the air itself (like the heaven) revolves in larger circles and therefore with greater velocity, there is found a constant and perpetual breeze blowing from east to west; so that they who want a west wind often seek for it and find it without the tropics. It appears therefore that this motion is not extinguished even in the lowest air; only it now becomes sluggish and feeble; so that it is scarce felt without the tropics. And yet even outside the tropics here in Europe, when the sky is calm and clear, there is observed at sea a certain breeze following the sun, which is of the same kind. And we may also suspect that what we experience here in Europe, where the east wind is keen and drying, whereas on the other hand the west is genial and moist, does not only depend on thisthat with us the former blows from the land, the latter from the sea; but likewise on this, that the east wind, being in the same direction as the proper motion of the air, stimulates and irritates that motion, and thereby dissipates and rarefies the air. The west wind, on the other hand, blowing contrary to the motion of the air, turns the air back upon itself, and thereby thickens it. Neither is that common observation to be despised, that the higher clouds generally move from east to west when contrary winds are at the same time blowing on the earth. And if this is not always the case, the reason is that there are sometimes contrary winds blowing, some above and others below; and those that blow above (if they be opposite) disturb the proper motion of the air. And therefore that this motion is not confined within the limits of the heaven is sufficiently clear.

Next in order is the second inquiry; namely, whether the waters move regularly and naturally from east to west? meaning by waters those collections or masses of water, which form portions of nature large enough to have a correspondence with the fabric and structure of the universe. And I am clearly of opinion that the same motion belongs to this mass of waters and exists in it, but that it is slower than in the air, though by reason of the grossness of the body it is more visible and apparent. Out of many experiments therefore which might be brought to prove this, I shall for the present

Acosta, Hist. des Indes, iii. 4.

content myself with three, but those ample and eminent, which demonstrate that this is the fact. The first is that there is found a manifest motion and flow of waters from the Indian Ocean to the Atlantic, and that swifter and stronger towards the Straits of Magellan, where there is an outlet to the west; and also a great motion in the opposite part of the world from the German Ocean into the British Channel. And these courses of water manifestly revolve from east to west. Wherein it is to be especially observed, that in these two places only the seas are open and can perform a complete circle; whereas on the contrary in the middle regions of the world they are cut off by the two obstacles of the Old and New World, and driven (as into the mouths of rivers) into the two channels of the Atlantic and Southern Ocean, which stretch from north to south, and therefore do not interfere with the order of motion from east to west. The true motion therefore of the waters is most properly taken from these extremities of the world which I have mentioned, where they are not obstructed, but pass through. This is the first experiment. The second is as follows:

Supposing that the tide at the mouth of the Straits of Gibraltar comes in at a certain hour, it is plain that it must come in later at Cape St. Vincent than at the Straits; later at Cape Finisterre than at Cape St. Vincent; later at Ile de Ré than at Cape Finisterre; later at Noirmoutier (insulam Hechas) than at Ile de Ré; later at the mouth of the English Channel than at Noirmoutier; later on the coast of Normandy than at the entrance of the Channel. And so far it is regular; but at Gravelines the order is completely changed (and that with a great leap), the tide coming in at the same time as at the mouth of the Straits of Gibraltar. And this second experiment I refer to the first. For I conceive (as I before said) that in the Indian and Northern Oceans the proper course of the water from east to west is open and perfect; whereas in the channels of the Atlantic and South Sea it is straitened, thwarted, and repelled by the opposition of land, which on both sides stretches along from north to south, and gives no free outlet to the waters, except towards the extremities. But this compulsion of the waters from the Indian Sea to the north, and that from the German Ocean to the south, differ immensely in

extent by reason of the different force and quantity of the waters. And hence all the Atlantic Ocean as far as the British Channel yields to the force of the Indian Ocean; while only the upper part, namely that which lies towards Denmark and Norway, yields to that of the North Sea. Now this must be so. For the two great islands of the Old and New World are by shape and position broad at the north and pointed at the south; so that the seas towards the south occupy a large space, but the seas towards the north (at the back of Europe, Asia, and America) a small one. Therefore this great mass of waters, which comes from the Indian Ocean and is driven back into the Atlantic, is able to force and push on the course of the waters by a continued succession towards the British Channel, which is a succession towards the north. But that far smaller portion of waters which comes from the North Sea, and has likewise almost a free outlet in its own course towards the west at the back of America, cannot drive the course of the waters towards the south except at the point I have mentioned, about the British Channel. Now it needs must be that between these opposite motions there is some point where they meet in conflict, and where the order of the coming in of the tide is at once changed; as we said happened about Gravelines, which is the point where the currents of the Indian and Northern Sea meet. And that there is a kind of eddy from the contrary tides about Holland has been observed by many, not only from the inversion of the order of the hours of high water (which I have mentioned), but likewise from particular and visible experiment. But if this be so, it returns to this; that it must needs be that the further the parts and coasts of the Atlantic stretch southward and approach the Indian Ocean, the earlier does the flow of the tide become in point of precedence, inasmuch as it arises from the proper motion of the Indian Sea; but the further they reach to the north (up to the common point, where they are repelled by the contrary stream of the Northern Sea), the later in subsequence. But that this is so, that experiment of the progression from the Straits of Gibraltar to the British Channel plainly shows. Wherefore I judge likewise that it is high water earlier about the coast of Africa than about the Straits of Gibraltar; and reversing the order, that it is earlier about Norway than about

« AnteriorContinuar »