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with a velocity of forty miles per hour to blow over it from one end to the other, we have, no doubt, approximately the conditions under which Dr. Newberry made his observations. Such a wind, then, causes a surface gradient in Lake Erie of four feet in two hundred miles. The first effect of the wind is to drive the surface water from one end of the lake toward the other, and thus to cause a gradually increasing surface gradient. The difference of pressure arising from this gradient causes a counter-current in the lower strata of the lake, and the static condition with regard to change of gradient takes place when the force arising from this gradient is sufficient to overcome the friction, and maintain a countercurrent sufficient to return the water below just as fast as it is driven forward above by the wind. This is required to satisfy the condition of continuity, a condition which, in all such cases, must be satisfied after the maximum gradient has been reached, and there is no further accumulation of water at the one end or a diminution at the other.

The force of the wind is applied directly to the surface only, but is communicated to the strata below by means of the friction between the successive strata of gradually decreasing velocities with increase of depth in the upper strata, and gradually increasing velocities in the contrary direction at depths below the neutral plane which separates the direct from the counter currents. If we assume, as usual, that friction is proportional to the relative velocities between the strata, then, in order to distribute equally the force at the surface to the strata below, it is necessary for these relative velocities to decrease in proportion to increase of depth, and finally vanish; and consequently the absolute velocity must be comparatively very great at the surface, and diminish, rapidly at first and then gradually less, until the neutral plane is reached, when this velocity vanishes, and changes sign at lower depths. Since the direct velocities in the upper strata are very great in comparison with those of the retrograde motion below, it is evident that the neutral plane cannot be at any great depth in comparison with the whole; since where the velocities are least the transverse sectional areas must be greatest, in order that there may be as much flow in the one direction as the other.

Upon the hypothesis of no frictional resistance from the bottom to the counter-flow below, the relative velocities between the strata would vanish, and the maximum velocity of the counter-current would take place, at the bottom. In this case the force by which the water, held at a certain gradient by the force of the wind, tends to be restored to its level, is an exact measure of the force of the wind. This force, it is well known, is measured by the product of the mass into the acceleration of gravity along the descending gradient. But the mass for the same lake being proportional to the depth, and the acceleration proportional to the gradient, a relative measure of the force of the wind is the surface gradient multiplied into the depth. For the same wind, therefore, the gradient is inversely as the depth.

In the case of frictional resistance to the countercurrent at the bottom, as there always is, of course, the maximum velocity of the counter flow, and the vanishing of the relative velocities, take place at a plane a little above the bottom; and in this case the static gradient must be such that the force arising

from it must not only be sufficient to overcome the force of the wind, as communicated by friction to the several strata down to the plane of the greatest velocity of counter-flow, but likewise to overcome the friction of the bottom, communicated in like manner upward to the strata above, as far as to the plane of greatest velocity of counter-flow, where the relative velocities vanish, and where, consequently, the effect of friction from the bottom must stop. But this is small in comparison with the whole force, and for different depths is proportional to the gradient. We therefore still have, for a relative measure of the force of the same wind, in the case of varying depths, the product of the gradient into the depth, and consequently the gradient inversely as the depth.

If, then, we suppose the depth of Lake Erie to be increased 60 times, or to the depth of 12,000 feet, a wind with a velocity of 40 miles per hour would cause a gradient of only the one-sixtieth part of the observed gradient, or 0.8 of an inch, in 200 miles; but, on the other hand, if the depth were less, the gradient would be proportionately increased. Hence it is seen how greatly the gradient, and consequently the change of sea-level, belonging to a given wind, depends upon depth. But the difference of sea-level, of course, other conditions being the same, is proportional to the length. Hence, if we increase the length of the lake 15 times, or to a length of 3.000 miles, the difference of level then would be 15 times 0.8 of an inch, or one foot With the depth increased 60 times and the length 15 times, we have approximately the conditions of a section of the Atlantic Ocean extending from New York harbor to the coast of France; and a westerly wind. therefore, of a velocity of 40 miles per hour, would cause the sea-level to be one foot higher at the latter place than at the former. But the average wind blowing across the Atlantic we know is very much less than this, and therefore its effect cannot be nearly so great as this.

The mean annual velocity of the wind across the Atlantic in middle latitudes is approximately known from the mean barometric gradient. The difference between the annual mean of the barometer at Iceland and the parallel of 35° is about 10 millimetres; and this gives a gradient on the parallel of 45° which corresponds to a westerly wind of about 8 miles per hour. The relation between wind friction upon water and the velocity of the wind is somewhat uncertain; but it increases at least at as great a rate as the first power of the velocity, and probably at a rate considerably greater. But, assuming it to be as the velocity, then the average westerly wind between America and France causes a difference of sea-level between the two of only 2.4 inches. If wind-friction were as the square of the velocity, it would be only a half-inch. It undoubtedly falls somewhere between these two values, but even by the former the effect of the average wind in causing a difference of sealevel is very small.

But there is another argument, entirely independent of the observations on Lake Erie, or any absolute wind velocities, from which we deduce about the same conclusions. It is well known from barometric monthly averages that the barometric gradient between Iceland and the parallel of 35° is at least twice as great, on the average, in January as in July. Whatever the absolute velocities of the wind corresponding to given gradients may be, we know that they are proportional to the gradients, and conse

quently the westerly winds must be at least twice as strong in January as in July, notwithstanding Dr. Newberry seems to think there may not be much difference. If the annual average velocity of wind. therefore, whatever it may be, causes a difference of level between America and France of 2.4 inches, then this difference in January is 3.2 inches, and in July only 1.6 inches, and consequently a change of difference of sea-level of 1.6 inches between the two seasons. The discussion of long series of tide observations on both sides of the Atlantic gives a small annual inequality of sea-level with a range of several inches; but both the ranges and the epochs of maximum height of sea-level are nearly the same on both sides, the latter occurring in the fall; and so there can be, at most, only a very small change between January and July, not possibly as much as 1.6 inches, and therefore the average wind of the year cannot cause a difference as great as 2.4 inches, deduced from the preceding argument upon the hypothesis that wind-friction is in proportion to the velocity. It is admitted that some of the data upon which these results are based are somewhat uncertain; but if some of them are in error, a fourth or even a third part, it affects the argument very little.

Upon the usual assumption that friction between the different strata of water is proportional to the relative velocities without regard to difference of pressure at different depths, it is readily inferred, from what precedes, that the absolute surface velocity is independent of depth of water, and so a westerly wind of 40 miles an hour across the Atlantic would give rise to the same surface velocity as on Lake Erie. Dr. Newberry has not furnished us with any observation of surface velocity, and therefore we cannot infer what the velocity of surface water on the Atlantic, corresponding, say, to the average velocity of about 8 miles per hour, would be. This, if wind-friction is proportional to the velocity, would be one-fifth of that on Lake Erie corresponding to a velocity of 40 miles per hour. If the wind does not blow the water against a barrier, but in circuits, of course the case is very different.

In the trade-wind latitudes the westerly component of motion is perhaps about the same as the easterly component of the middle latitudes in the North Atlantic; and, as the tropical sea between Africa and the Gulf of Mexico is much deeper, we may infer, from what precedes, that the trade-winds cannot possibly cause a difference of sea-level of two inches, and hence raise the level of the Gulf of Mexico as much as one inch above the normal undisturbed level. The winds, therefore, can have no sensible influence in producing the Gulf Stream, for this deep and rapid current can only be caused by a difference of sea-level between the Gulf and the parts in higher latitudes toward which it flows.

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equivalents of those in Pennsylvania; but, in place of striking oil, there was developed a remarkable gas-well, which has been described by tourists and scientific men as a geyser of great violence. A full account of all the wells has been published in the Ohio state geological survey, and quite recently in the tenth volume of the Tenth census of the United States, by Prof. S. F. Peckham.

Some of the wells discharge a few gallons of oil each day, of a superior lubricating quality, gravity 32°.

The analysis of the gas is as follows:
Marsh-gas..

Ethyl hydride... Nitrogen.. Oxygen...

Carbon monoxide. Carbon dioxide....

81.4

12.2

4.8

0.8

0.5

0.3

100.0

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The pressure on these wells is not the same in all. There is a pressure for each well; at which degree of pressure there is an equilibrium between the generation or discharge of the gas, and the well's state of rest or quiet. Very little salt water is found in these wells, and it gives little trouble. Observations show that the supply increases in warm weather and in the heat of the day, and regularly with the variations of the moon, being strongest at the full moon. The gas is a rich illuminating hydro-carbonaceous gas, and, even when mixed with seven parts of atmospheric air, is a good illuminant. Well No. 2 has been systematically examined; and there is no apparent diminution in the supply of gas, during the past fourteen years of the twenty years the well has been blowing.' Where is it from?

That there is a limit to the supply of petroleum or gas cannot be questioned; but, with proper scientific and economical use of wells and territory, the life of a well can scarcely be measured or computed it is too great in quantity, and too long in time.

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Fresh water will drown out' a well. Will not holding a well under pressure until its equilibrium between a state of rest and production is about established, injure the well? It is an injury; therefore transporting gas through long lines of pipe, by an initial potential force amounting to several hundred pounds' pressure at the wells, is not the correct way. There is a reduction of pressure of about eight pounds to the mile in pipes. For long distances it will be proven that gas can be blown more economically, and to better advantage to wells and transportation, through the pipes, than be forced by its 1 Including the C and H of 0.024 solid hydrocarbon.

2 These gases were doubtless partly formed from solid carbon and occluded oxygen by the heat applied in vacuo.

initial pressure. The use of a fan-wheel may be applicable.

Although here, in and about this circle in the said map, no paying oil-well has been struck, nor does any great gas-gusher' 'blow,' yet good oil-sands, saturated with petroleum, are found, and a gas-belt is developed of most remarkable persistency and continuance; and the separated and scattered wells demonstrate a territory in which good paying oil and gas wells are liable anywhere to be struck. This territory embraces about the highest lands above Lake Erie, in the state of Ohio. This region gives proof of an abundance of gas for ages to come, for the supply of the surrounding manufacturing towns for light and heat.

The location of 'Neff's gas-wells' is in the eastern part of Knox and the western part of Coshocton counties, O. PETER NEFF.

Gambier, Knox county, O., July 15.

A remarkable swarm of Sciara.

In Psyche for September, 1880, Dr. Hagen, in discussing a swarming species of Sciara from South Carolina, made the statement, based upon Weyenbergh's list of swarms of Diptera (Tijdskrift v. entom. 1861), that the swarming of Sciara is new. In the American naturalist for February, 1881, Professor Riley states that he has frequently observed them in swarms so dense as to appear at a short distance like smoke, and quotes a letter from Dr. S. S. Rath von concerning the swarming of a species of this genus in the upper room of a building in Bethlehem, Penn, where they were observed to issue between the floor-boards. These records indicate that some interest will attach to the following facts:

Tuesday evening. July 20, I was sitting in my library of the second floor, when I became conscious of a humming noise, as of a distant army of flies. The noise gradually increased for nearly half an hour, when I went to the window to investigate. Outside I heard only the customary night noises; but, as I drew my head in, I saw that the ceiling of the library was covered with tens of thousands of minute midges of the genus Sciara. Except immediately above the lamp, the white ceiling was tinted brown with them. They made no attempt to reach the light, but clung to the ceiling around the edges of the room, extending down on the walls for several inches, and massed a dozen or more deep in the angles. All were in constant motion, and the noise was loud enough to drown the sounds of the crickets and tree toads outside. The sound, as a whole, was a distinct musical note, varying but a fraction of a whole tone, and corresponded, as nearly as I could place it, with E flat above middle C. The number was beyond compute I at once closed the windows, and in ten minutes they became almost opaque from the numbers which settled upon them. On going below stairs, I found, that although doors and windows were open, and a bright light was burning, very few of the midges had entered. I easily rid the library of those which had entered, by lighting a spoonful of pyrethrum in my ash-receiver. They fell as fast as snowflakes, and in the morning were swept up by the dustpanful.

The house is a new one, finished in April last, and is situated on a level, nearly clear plateau on Washington Heights. The gnats entered only at the second

story windows. The night was clear and not sultry, and the wind was north-east. Later in the evening a heavy shower fell. The midges were not noticed on previous or succeeding nights. From these facts it seems quite plain that the gnats were flying in au immense swarm at some distance from the ground, and either met the house in the direct course of their flight, or were attracted from their regular route by the light. L O. HOWARD.

Washington, July 23.

Another carnivorous rodent.

Over a year ago I recorded in this journal the carnivorous habits of several of the Rodentia (Science, v. No. 114). In that communication I called attention to the meat-eating propensities of the muskrat (Fiber zibethicus), and a species of fieldmouse, that I then had in captivity. Since writing that, I have described the field-mouse, for it proved to be a new species, and it is now known as True's Piñon mouse (Hesperomys truei). No doubt others of the same genus will be found given to a similar diet when the opportunity offers. But here comes another rodent that strongly asserts his taste in that direction, and will consume raw meat even in preference to his regular diet list, as we have always conIceived it to be. This is no less an animal than the prairie dog' (Cynomys ludovicianus). I have at the present writing a pair, half-grown, of these engaging little pets; and for the last two days they have been fed on raw meat, refusing their ordinary food served to them at the same time. They tell me that the Navajo Indians, when they keep them in captivity, feed them with raw meat half the time, and the little marmots eat it with avidity.

As I have noticed elsewhere, rats will devour raw meat whenever they can get it, and usually in prefer ence to other things.

In time, no doubt, it will be proved that it is a universal habit of the order Glires. R. W. SHUFELDT.

Fort Wingate, N. Mex., July 16.

Germ of hydrophobia.

I see in your issue of July 9, p. 23, that the credit of having at last discovered the germ of hydrophobia is claimed by the London Lancet for Dr. Dowdeswell, who finds it in a micrococcus in the medulla and spinal cord of animals affected with this disease.

I do not remember that the attention of your readers has been drawn to the fact that this discovery had been previously claimed, with much show of reason, by Professor H. Fol of Geneva (Archives des sciences, vol. xiv. p. 449, 1885, and vol. xv. p. 414, 1886). According to Fol, also, it is a micrococcus found only in this disease, and so minute that it requires a good objective to see it at all. Of this micrococcus he has made pure cultures, which by inoculation communicate the disease with certainty. Berkeley, Cal., July 19.

A bright meteor.

JOSEPH LECONTE.

The meteor recorded by Mr. Brackett as having been seen at St. Johnsbury, Vt., on the night of Aug. 11, agrees as to size and direction, as well as date and time, with one seen at Salem, Mass.

E. S. M.

SCIENCE.-SUPPLEMENT.

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WHEN the editor of Science invited me to take part in a discussion upon economic principles and methods, I at first declined, because of my doubt whether any fruitful results would follow; and my final acceptance was due to the thought that the professed economists in this country were not so widely apart in their views as the expression which they sometimes use would seem to indicate, and that through discussion they might perhaps become better acquainted with each other's purposes and methods. It would be premature to say that there is no hope of realizing such an expectation, although the rigidity with which the lines between the old and the new in economy are drawn is not very encouraging. Nor is this impression wholly the result of the aggressive statements of the representatives of the 'new school; ' the criticisms offered by Mr. Hadley under the title Economic laws and methods,' present views which by universal consent are the exclusive property of the old school.'

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Mr. Hadley's paper is professedly a criticism upon my presentation of the relation that exists between economics and jurisprudence, but it suggests much more than was directly touched in that discussion; and, in meeting the editor's request for a 'reply,' I may perhaps be permitted the same liberty, and state, in as concise a manner as possible, the views which I hold respecting the nature and purpose of political economy, and the method of study which its profitable prosecution imposes.

If asked to define political economy, I should say that political economy treats of industrial society. Its purpose as an analytic science is to explain the industrial actions of men. Its purpose as a constructive science is to discover a scientific and rational basis for the formation and government of industrial society.

But, it may be asked, under what conditions can political economy be said to have attained its scientific purpose? When is an industrial fact satisfactorily explained? I answer, when it is referred to some general truth which, either for the sake of convenience or because our limited intelligence will not permit us to press the inquiry further, must be regarded as final. Truths of this sort

are fundamental in economics, and are capable of being classified under three heads. (a) The first class embraces what is ordinarily called the laws of human nature. Such truths are discovered by a study of one's self, by a study of history, and by a study of statistics. There can be no quarrel between the old and the new economists as to the propriety of admitting such facts. The quarrel begins when the members of the old school assert that a few simple laws of human nature' furnish adequate material out of which to construct an economic science capable of explaining all industrial facts. (b) The truths of physical nature to which all industrial activity must conform are likewise final for purposes of explanation. Why do men go west to take up new lands? Because, to quote from Mr. Hadley, they desire "to obtain the maximum of satisfaction for the minimum of sacrifice." This, however, does not explain the fact of migrations. One does not understand why a given quantity of satisfaction can be secured for less sacrifice by an agriculturalist in the west than if he increased the numbers already living on the lands of the east, until he discovers the physical law of the productivity of land known as the law of diminishing returns. Again, it is an industrial fact that the Christian world is growing rich. Is it enough to trace this fact to the permanent desire on the part of men to grow rich? Do we not understand it better when we learn that the latent energy in a ton of coal is equal to eleven million times its own weight, and that the available energy when the best machines are used is equal to one million times its own weight? If, then, physical laws are essential to a satisfactory explanation of industrial facts, and if such explanation is the scientific purpose of economics, are we not justified in admitting such physical laws as material for the construction of the science? But, says the objector, English economy recognizes physical laws. The law of diminishing returns is called by Mr. Mill the fundamental law of economy. This is certainly true, and this is why it is so difficult for me to understand the plan of architecture according to which English economists have built their science. I cannot appreciate the necessity of bringing in at the back door any facts essential to the explanation of industrial phenomena. (c) The third class of final truths is disclosed when once the explanation of observed facts is traceable to the legal structure of society. Why were wages in England between the years

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1200 and 1400 permanent? Why has the principle of competition exerted a greater influence since 1500 than before? Why in the year 1800 in England was the woollen industry largely controlled by journeymen, while in the cotton industry the majority of workers had never served an apprenticeship? If these questions are not legitimate ones to put to the economist, I do not know who is to deal with them; nor do I know how he can answer them except by referring them to the legal structure of society which prevailed at the time considered. For the same reasons, therefore, as were presented above, the lego-historic facts to borrow a phrase from Lasalle are material out of which to construct an economic science. It is true that such facts are not permanent, and when we call a truth which rests upon them a final truth, our language must be accepted with limitations; but it is a distinctive feature of the historical school to recognize limitations in periods studied. Its members are not ambitious to cover all times and all peoples with their generalizations, for they well know that such generalizations would be too thin for any use. I have brought this classification prominently into view, because Mr. Hadley insists so strongly that economics "is built out of a few simple laws of human nature," and criticises me for adding to this, as equally necessary for explaining the phenomena of industrial society, the physical and legal surroundings of men. The expression used in my former paper must have been loose, or so candid a critic and so clear a thinker would not have thus shot by the mark. And I am inclined to the opinion also that the real difference here brought to view pertains primarily to form of presentation; its discussion, therefore, would be scholastic rather than scholarly.

Still there are certain radical differences between the views expressed or implied in Mr. Hadley's paper and those which I entertain; and, should circumstances ever render it necessary for me to nail a thesis on his lecture-room door, it would include the following protests.

I protest, in the first place, against such free and unguarded use of analogy as argument. Because certain things are true in physical science, it does not follow that similar things are true in social science. One may be well versed in the methods of successful investigation in the physical sciences, and yet not possess the mental equipment necessary to arrive at truth through the intricacies of social relations. And why? For two reasons. the one case, the forces considered are permanent and reliable; in the other, some of the forces are subject to constant variation. Development of a physical science consists in the discovery of truths

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which are assumed always to have existed, nor has such an assumption so far in our experience proved the source of error. Development of a social science, on the other hand, consists partly in the new discovery of old truths, and partly in observing new truths to emerge from the growth of the social organism. If this be true, is it not illogical to rely upon analogy? Again, the study of physical science is not complicated by the fact that the forces considered have a conscious purpose, and, within limits, are self-directing. But in social sciences this is unfortunately the case, at least the theory of social science with which the latest phase of economic science allies itself holds strenuously to the idea of a self-conditioning social organism. In this respect, therefore, analogy fails.

I protest, in the second place, against the relation that is assumed to exist between the science and the art of economics. It appears to me that they who make most use of these phrases fall also into the error of relying too implicitly upon analogy. What is said of the bearing of a science on an art, which is quite fruitful when applied to a physical science and the art of mechanical invention, ceases to have any clear-cut meaning when imputed to social relations. The reason is, that what is termed the art of economics' is itself one of the elements which must be admitted by the science of economics' in order to explain the laws of its own development. If this be true (and it must be admitted if society is an organism of conscious purpose), there is no such sharp line of distinction between the science and the art of economics as has been commonly supposed. Without denying an element of truth to what Mr. Mill so admirably states in the last book of his 'Logic,' I still insist that it is preferable to speak of a science of economics which is at the same time analytic and constructive.

I protest, in the third place, against the use of the astronomical method of investigation in the social sciences. Should my readers desire to know in what this method consists more perfectly than may be learned from Mr. Hadley's paper, they will find it presented at length in Cairnes's 'Logical method of political economy.' Indeed, that book might well be termed a handbook for the use of students in economic observatories. The method, in short, consists in this: to build a system of thought on the assumption that a certain line is straight, and then to take a squint to see how crooked it is. I would not, of course, deny that this method is, in itself considered, logical, nor that it is fruitful when employed in astronomy: my only objection is, that in economics it is of no sort of use. It has not led to a single

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