Imágenes de páginas

the expansion at each point. Thus from the pole to the equator a spheroidal meniscus would be spread equal to the ocean expansion under the solar heat. It is a remarkable feature that the heating leaves each vertical ocean column of its original weight, and there is thus a perfect mechanical equilibrium between these columns considered as joined by their interior bases. Thus considering the grand ocean masses, there is no disturbance of static stability from the heating agency of the sun, hence there is no formation of massive currents due to this cause.

If now we regard the heated ocean in its hydrodynamic aspect, we find that the bounding surface having everywhere a slope toward the pole exceeding that of the normal level surface, there remains an unresisted surface tendency towards the pole which primarily tends to produce a superficial flow from the equator polewards. This gives manifestly but a slight disturbance of normal level, amounting in the meridian quadrant only to the vertical expansion at the equator, and being diffused over the entire quadrant. It is extremely doubtful if this would suffice to overcome the passive resistances and produce an actual surface overflow. If, however, a current were once established by any other agency, such as the wind, the equatorial heating would constantly operate to maintain this current. The heated waters would constantly be lifted as a floating mass on the colder waters which, pushing on the lighter equatorial mass at its base, would come in to replace any deficiency of mass due to the superficial outflow. Taking the facts as they are, we find in the trade-winds and the resistance of the continents, two causes fully adequate to break up the static equilibrium referred to, and obviously giving the precise direction to the outflow which it actually has. Thus while the type of action induced by the solar heating power considered along the meridian is surface outflow and deep inflow, the perennial trades determine this circulation along a different and constant route, fixed first by continental obstructions, and essentially modified in direction by the earth's rotation.

As the equatorial evaporation greatly exceeds the corresponding rain fall, this operates to counteract in part the regular out. flow by diminishing the quantity of water to be discharged on account of expansion due to heating. This would also increase the saltness and specific gravity of the equatorial waters, and to that extent would bring their actual surface into close accordance with the normal level. It is clear that this saltness could not fully compensate for the expansion by heating, or we should have the surface reduced to the normal level, when all would either be in stable equilibrium, or below it when the currents would be reversed.

It thus appears that the expansion due to equatorial heats in. duces a superficial derangement tending to an outflow towards the poles, which by the trade winds and continents is determined along a single line of debouche. This gives a discharge with far less frictional resistance than a direct meridional outflow would encounter, as this would involve a polar set for the entire ocean surface.

Accepting the well-determined trade-winds and the equatorial current as certain facts, we shall find that the vast surface sheet of water which has a westerly set under the trades, having acquired a very considerable velocity, becomes the representative of a vast amount of living force. When by impact against western barriers this vast sheet of water undergoes inflection to the north or south, it still retains the greater portion of its living force, and will continue to do so until this is wholly expended in overcoming resistances. If now we bear in mind that the wide equatorial sheet is by this deflection consolidated into a compact current of deep section, and also that the resistance per mile is proportionate to the length of the line of frictional resistance in a cross section, we shall see that the currents turn towards the poles with their forward impulse almost unabated, and with the resistances greatly reduced. We ought, therefore, to expect that the inertia of this vast moving mass would suffice to carry it on with a mean velocity, slowly abating, to the polar regions. So soon as the progress of the current gives it an increasing latitude, the effect of the diminishing parallels in giving an eastward trend would show itself; and, combined with the forward projectile motion of the mass of waters, would determine the route of the current, governed, of course, by solid opposing masses of continents, islands, and shoals.

Reaching the artic neighborhood, this current would fall in with the tendency to restore to the equatorial region the waters withdrawn by outflow, which thus leave a deficiency of static mass in that region. Its forward force not yet expended, would bring it into the equatorial flow only after a long arctic sweep. Then bordered in by the eastern occean coasts, it circles on to the equatorial belt, there to start the repetition of its course either directly, or by proxy, if, entering at great depths, it serve only to lift higher portions above the normal level. We have thus a continuous circuit in which the water whirls under the primary impulse derived in the equatorial regions, an outflow due to heating and the direct propulsion of the trade-winds. The primary order of circulation is in two currents, the upper running polewards, and the under from the poles to the equator. This order is entirely modified by the action of the trades, and becomes essentially a horizontal circulation, the propelling action of these perennial winds, conspiring with the outflowing declivity to determine an immense movement, of which the living force imparted in the equatorial region suffices to carry on the circuit in full and enduring activity.

This consideration of the effect of inertia in storing the living force of this immense equatorial current, and thus enabling it to sweep through the cycles of the seas, has not been duly consid. ered. These currents, in such a place as Florida Straits, move in a closed channel, and are subject to the hy.lrodynamic rules for this case. The gradual changes of direction and velocity there imposed, produce less absolute resistance than is generally imagined, by reason of the great mass of waters relative to the area of frictional surfaces.

The problem of ocean currents is of very great complexity, not only on account of the difficult hydrodynamic questions involved, but because the effect of the winds on the ocean surface can scarcely be subjected to estimation. The permanent elevation of the equatorial waters above the normal level traced from the pole, might be approximately determined by knowing the mean equatorial ocean temperature at all depths, and the same from point to point towards the poles, accompanied with observations on the corresponding saltness. Were there a considerable deficiency of weight in the vertical equatorial column, relative to an arctic one, connected by their bases at the same deep level, this would at once generate a corresponding wave towards the equator. As we may be sure that the equatorial mean ocean temperature exceeds the artic mean temperature, we must concede some elevation above the true normal level throughout all the warmer latitudes, but any attempt to definitely fix its amount, would be very rash in the present state of our knowl. edge.

There are numerous secondary points which might enter this discussion, but which need not now be considered. I will notice a slight oceanic oscillation which is practically unimportant; but which I believe has not before been noticed. The sun in its daily round must heat the waters of the sea, at a given locality, in such a manner that there shall be a daily maximum and minimum sca temperature due to absorption and radiation combined. This must give a maximum and minimum of expansion, or a species of tidal wave would follow the sun, which might well be called the heliothermal tide. It would clearly be too minute for separate observation, and though curious, cannot be important.

Another circumstance is worth notice here. A forward cur. rent in the sea has a distinct bounding surface on which it encounters a frictional resistance. The mode in which this resistance is expended is by a constant dragging into the forward movement parts of the layer of water making the boundary of the current. Thus if a current be moving through a sea other. wise tranquil, it will by this lateral dragging carry forward such a volume of water in addition to its own proper mass, that a counter-current must set in to restore the level. This is, I supSECOND SERIES, Vol. XXVII, No. 80.-MARCH, 1859.

pose, the explanation of some of the counter currents which exist along the great oceanic currents, as also of the eddy currents of rivers. These too imperfect generalizations may do something towards making the system of ocean currents more comprehensible. So great a subject needs treatment far different from what it has yet received, and first of all the essential facts should be more clearly established. Unfortunately this can result only from long, well organized, and costly operations for this express purpose. We must be content to do our several small parts patiently, hoping for more light in the future.

ART. XX.- Report on Dupont's Artesian Well at Louisville, Ky.;

by J. LAWRENCE SMITH, M.D., Prof. Chem. University of Louisville.

This work was commenced in April, 1857, from the bottom of a well that had a depth of 20 feet, the boring tools employed made a hole 5 inches in diameter to the depth of 76 feet from the surface; the boring was now reduced to 3 inches, and thus continued to the bottom of the well. The depth of well is 2086 feet; flow of water 330,000 gallons in 24 hours; rise above the surface 170 feet.

The rock struck, which geologically belongs to the Devonian series, is for 38 feet shell limestone; then for 40 feet coralline limestone; at which depth the Upper Silurian is reached. Without being able to make out with any degree of certainty, the amount of Upper Silurian passed through, we suppose it to be over 1200 feet. At the depth of 1600 feet a sandstone was reached, doubtless of the Lower Silurian, and 97 feet deeper was encountered the first stream of water which reached the surface. This flowed out abundantly and with much force. The quantity not being sufficient, the boring was continued. After this, it was unnecessary to use the bucket to take out the material detached by the borer, the force of the water bringing up the fragments very readily. The water increased in quantity in going deeper, the increase being more marked at 1879 feet, and still more at 1900 feet, where pieces of rock weighing an ounce or two came up with the water. The water increased every ten or twenty feet to the depth of 2036 feet; here a very hard magnesian limestone was encountered 6 feet in thickness. After which the sandstone reappeared, and for the next 50 feet there was no increase of water.

The following table exhibits the series of rock as far as it is possible to make it out by the fine fragments taken out at different depths, beginning at the top:

76 feet, sand and gravel. 100 feet, tolerably pure limestone, with fragments of fossils. 12 feet, soft limestone mixed with clay. 52 feet, tolerably pure limestone mixed with fossils. 5 feet, limestone with ferruginous clay. 81 feet, gray limestone. 157 feet, limestone mixed with clay. 149 feet, tolerably pure limestone with many portions quite white. 13 feet, clay shale with little calcareous matter. 207 feet, limestone with a little blue clay shale. 33 feet, same, little darker and more shale.

Next 94 feet, pure, very white limestone with fossil alternating with very dark limestone, color probably from organic matter, with some dark shale.

26 feet, shaly limestone.
40 feet, very light and hard pure limestone.
i foot, white clay.
546 feet, gray limestone, alternating hard and soft.
41 feet, sand rock-white.
4 feet, same, very fine and hard, with little limestone.
60 feet, same, with more lime.
72 feet, same, less limestone.
308 feet, same sandstone with but little lime.
6 feet, magnesian limestone, very hard.
50 feet, sandstone again.

At the urgent request of many citizens of Louisville, the boring was now stopped to give a fair test of the medical virtues of the water that was pouring forth at the rate of 230 gallons per minute, or about 330,000 gallons in 24 hours. The water, by its own pressure, rises in pipes 170 feet above the surface.

The boring was accomplished in sixteen months, and the depth reached is 2,086 feet. In order to conduct the water to the surface and prevent its passing off into the gravel beds below, a tube five inches in diameter leads from the surface to the rock, a depth of seventy-six feet, into which it is driven with a collar of vulcanized gum elastic around it. No tubing is found necessary for any other part of the boring.

When the size of the bore (three inches in diameter) and its depth are considered, the flow of water from the well is unequalled by any other artesian well yet constructed that flows above the surface, for, although the Grenelle well at Paris delivers 600,000 gallons in twenty-four hours, it has at the bottom an area six times as great as the Dupont well, and a few hundred feet up seven times as great. A corresponding diameter to Dupont's well would, according to just and reasonable calculations, furnish about 2,000,000 gallons in twenty-four hours; also the elevation of the water above the surface is greater than that of any other artesian well, and it is only exceeded in depth by the St. Louis well, and that to an extent of 113 feet.

« AnteriorContinuar »