propriation of fifty thousand dollars to start the work, the entire cost of which is estimated at nearly six hundred thousand dollars.

Dr. George L. Fitch has for five years been in charge of the lepers in the Sandwich Islands. He gives it as his opinion, based on careful study and attempts to inoculate the virus into healthy persons, that leprosy is not a contagious disease.

A new and interesting form of stereoscope has recently been described by Mr. Stroh, before the Royal society of England. The apparatus consists of two dissolving-view lanterns placed side by side, each of which throws a magnified stereoscopic picture on the screen. In front of these lanterns there is a rotating disk, portions of which are cut away, alternately shutting off the picture from each lantern. By so arranging the rotating disk as to permit each eye to see only the view from one of the lanterns during its very brief exposure, a stereoscopic effect is produced, the impression of each picture remaining upon the retina of the corresponding eye long enough to appear to be continuous.

- Prof. Charles Upham Shepard, jun., has deposited his collection of meteorites in the national museum at Washington. The collection represents nearly two hundred distinct falls, and contains many exceptionally fine specimens. The iron from Dalton, Ga., weighing one hundred and seventeen pounds, is the largest meteorite in the display, and is almost perfect. Only a small piece has been cut from the lesser end.

Dr. William L. Dudley, late Miami medical college, Cincinnati, has accepted the chair of chemistry in Vanderbilt university, Nashville, Tenn.

- The volume of the Ray society (England) for 1885 is made up of the late Mr. Buckler's lifehistories of British butterflies, with colored plates of their earlier stages. Most of the descriptions have appeared piecemeal before; but the work is rendered more complete by additions from his note-book, and new observations by his friend and colleague, Mr. Hellins. Seventeen plates, with two hundred and fifty-five figures, are given, and the drawings are better than the average. The industry of Mr. Buckler, who made all the drawings, is shown in the remarkable fact that some part, at least, of the history, is given for fifty-eight of the sixty-three British species. It is a pity that no drawings whatever of eggs are given.

The lectures now being delivered at Oxford by Professor Sylvester on his new theory of reciprocants will appear in the coming numbers of the American journal of mathematics. The lec

tures are presented in quite simple style, and will be exceedingly interesting to all students of the modern algebra, or, more accurately, of the theory of invariants. The first eight or nine lectures will appear in the forthcoming number of the Journal, vol. viii. No. 3.

'Solar heat, gravitation, and sun spots,' by J. H. Kedzie (Chicago, S. C. Griggs & Co.. 1886), is certainly a book which deserves little praise. If one is not convinced by the title alone, he will find, in the rambling speculation of the author, sufficient evidence that he is treating of theories far beyond him, and of the history and development of which he knows nothing.

- The Sanitary engineer has collected and published in book form a number of articles which have appeared in that journal upon 'Steam-heating problems.' This collection is published partly because their previous book upon Plumbing and house-drainage problems' was well received. The book is intended to be useful to those who design, construct, and have charge of steam-heating apparatus.

Laboratory calculations and specific gravity tables,' by John S. Adriance (New York, Wiley), is intended to aid students and analytical chemists in their calculations. The author has collected those tables which are constantly needed in the laboratory, has edited them with care, and it is probable that the book will be found to fill its place satisfactorily.

Prof. B. O. Peirce of Harvard has recently published The elements of the theory of the Newtonian potential function' (Boston, Ginn), as he calls it. The book is made up of lecture-notes used by the author during the last four years, and can be used by those familiar with the first principles of the calculus. The author found it difficult to find in any single English book a treatment of the subject at once elementary enough and at the same time suited to the purposes of such as intended to pursue the subject further or wished without making a specialty of mathematical physics to prepare themselves to study experimental physics thoroughly and understandingly. The book is divided into five chapters, - on the attraction of gravitation, the Newtonian potential function in the case of gravitation, the Newtonian potential function in the case of repulsion, the properties of surface distributions (Green's theorem), and electro-statics. There are certainly few better able to produce such a book than Professor Peirce.

Messrs. J. B. Lippincott & Co. have in press a 'Manual of North American birds,' by the eminent ornithologist, Prof. Robert Ridgway, curator department of birds in the Smithsonian institution. The work is to contain some 435 illustrations suitably executed, and will conform to the geographical limits, classifications, numeration, and nomenclature adopted by the American ornithological union. We doubt not it will be a most important contribution to the literature of the subject, and presume that naturalist and sportsman alike will find in it an aid.

- Mr. N. S. Goss's revised list of the Birds of Kansas' gives notes on three hundred and thirtyfive species occurring in that state, one hundred and seventy-five of which are known to breed within its limits. This little work contains the results of a large amount of labor, and is highly creditable to its author.

-The young collector' (London, Sonnenschein & Co.) is the title of a very cheap and convenient series of small handbooks designed for the amateur, tastefully and neatly gotten up, and issued at one shilling each. Four of them, so far, have appeared, on Mosses,' by J. E. Bagnall; on 'British butterflies, moths, and beetles,' by V. F. Kirby; on 'Seaweeds, shells, and fossils,' by Peter Gray and B. B. Woodward; and on English coins and tokens,' by L. Jewitt and B. V. Head. These little handy handbooks contain simple directions for the collection and preservation of specimens, with a general introduction to scientific classification, habits, etc., interpersed with numerous engravings. To the boy or girl with an awakening propensity to collect (and every healthy boy at some period of his career has a more or less enduring hobby of some sort or other), these little works will serve as useful guides even in America. Why cannot some publisher get out similar and as cheap handbooks, more expressly serviceable for the young American collector?

The longest clock pendulum known is said to be one in Avignon, France, measuring sixtyseven feet, to which is attached a weight of one hundred and thirty-two pounds. Its movement is slow, passing through an arc of between nine and ten feet in four seconds and a half.

Mr. J. H. Long, in a recent paper on the microscopic examination of butter, arrives at the conclusions, that, “taking all things into consideration, we have no absolutely certain method of distinguishing between butter and some of its substitutes, and that, of all methods proposed, the microscopic are perhaps the least reliable." These conclusions are similar to the ones reached by Prof. H. A. Webster, but are directly opposed to those of Dr. Taylor.

during 1885 reached nearly seven thousand; and during the past six years nearly forty thousand dead horses were received at the receiving-docks.

Recent researches by Messrs. Coleman and McKendrick of England, on the effects of extreme cold on certain microbes, especially those concerned in putrefactive changes, show that the organisms are killed by exposure to a temperature of from 80° to 120° F. below zero, though their germs are unaffected, and speedily develop after an increase of temperature.

We learn from the Athenaeum that the necessary funds have been granted for the expenses of the British expedition to observe the total eclipse of the sun on Aug. 29. The party, which will probably include Mr. Maunder and Mr. Turner of the Greenwich observatory, will occupy three stations on the island of Grenada in the West Indies. Totality occurs there about quarter-past seven o'clock in the morning, and lasts very nearly four minutes. A proposal was made some time ago to despatch a German party to Benguela on the west coast of Africa, the most favorable point from which observations could be made; but we have not heard that it has assumed a tangible form. The bill introduced in congress for fitting out an American expedition seems to have been buried with some committee, and it is now, of course, too late for proper preparation, even if the bill could be pushed through.

The president of the province of the Amazonas, Brazil, has authorized the employment of Francisco Pfaff, of Geneva, Switzerland, as the chemist of the botanical gardens established at Manaus a few years ago. It will be the duty of the chemist to study and report upon the medicinal and industrial properties of the plants of the Amazon valley.

LETTERS TO THE EDITOR.

Correspondents are requested to be as brief as possible. The writer's name is in all cases required as proof of good faith.

Sea-level and ocean-currents.

THE subject of sea-level and ocean-currents is not so simple that there is not room for differences of opinion. It is not to be denied that exceptionally strong winds, such as Texas northers or those of violent cyclones, often cause considerable changes of sea level in shallow water like that of Lake Erie, or of the thin stratum of the same depth, and much less near the shore, along the Atlantic coast and the border of the Gulf of Mexico, extending mostly to a distance many miles from the coast, where the bottom of the shallow water drops off abruptly into deep sea-water. But the effects of winds of the same strength upon deep sea-water are comparatively very small.

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 vasishes, 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 conseJULY 30, 1886.]

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 The discussion of long series of tide obserseasons. vations 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. WM. FERREL.

Washington, July 18.

Neff's gas-wells.

Marsh-gas.... Ethyl hydride... Nitrogen......... Oxygen........... Carbon monoxide Carbon dioxide...

81.4

12.2

4.8

0.8

0.5

0.3

100.0

Carbon 1.....

Hydrogen 1........... Nitrogen...... Carbon monoxide 2. Carbon dioxide ..... Water.

Ash (Fe2O3 and CuO).

95.057

0.665

0.776

1.3:8

1.386

0.682

0.06

100,000

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.

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 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. Rathvon 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. LO. 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 conceived 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. JOSEPH LECONTE.

Berkeley, Cal., July 19.

A bright meteor.

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.