many were those of long-legged wading birds. But the most interesting are those of the Mammoth and the problematical so-called human tracks. About the Mammoth tracks there can be no doubt. Some of these were uncovered by blasting in my presence; round basin-shaped impressions, 5 inches deep and 22 inches across, and occurring in regular alternating series, the hind-foot tracking almost perfectly with the fore-foot. The nature of the so-called human tracks, however, is far more doubtful. These occur in several regular alternating series of 15-20. In size they are 18-20 inches long, and 8 inches wide. In shape they are many of them far more curved than the human track, especially in soft mud. The stride is 2 to 3 feet, and even more. The outward turn of the track is in many cases greater than in human tracks, especially in soft mud. But the most remarkable thing about them on the human theory is the straddle, i.e. the distance between the right and left series. This I found to be 18 and even 19 inches, which was fully as great as that of the mammoth tracks. This is probably the greatest objection to the human theory. On the other hand, the great objection to the quadrupedal theory is the apparent singleness of the tracks, and the absence of claw-marks. But it must be remembered that the tracks are deep, and the outlines somewhat obscure, and also that the mammoth tracks, on account of tracking of hind with fore-foot, are in most cases, though not always, single. After careful examination for several days, the conclusion I came to was that the tracks were probably made by a large plantigrade quadruped, most likely a gigantic ground-sloth, such as the Mylodon, which is found in the Quaternary, or the Morothenium, which is found in the upper Pliocene of Nevada. The apparent singleness, the singular shape, and the large outward turn of the tracks I attribute to the imperfect tracking of hind and fore-foot on the same side, while the absence of clawmarks was the result of the clogging of the feet with mud. This view seems to me most probable, but many who have seen the tracks think them human, and I freely admit that there is abundant room for honest difference of opinion. On any theory the tracks are well worthy of scientific attention. Berkeley, California, May 12 JOSEPH LE CONTE Cloudiness of Aquarium CAN you tell me the reason why the water in my fresh water aquarium will not remain clear, but becomes cloudy throughout in a few days after filling. The aquarium in question holds about twelve gallons of water. It stands in a window facing north. I have in the water two or At the bottom three water-plants, among them a water-aloe. are small gravel stones, which have been thoroughly washed before using. Floating on the surface for the benefit of a few newts is a piece of virgin cork, on which is placed some carpet I had a dozen minnows and four newts to begin with, but nine of the minnows and two of the newts have died, manifestly from the fouling of the water. moss. So far as I can judge from "X's" description, the cloudiness of the water in his aquarium is due to the abnormal development of some unicellular algal (Palmellaceae) or to the prolific spore-production within it of one of the filamentous forms (Confervaceæ). This may be obviated by screening the back of the tank from the access of light. Possibly "X" may find on examination that the cistern whence he obtains his supply has been left uncovered, and that the intruding algal has established itself and entered upon the reproductive process in that position. In that case he should either isolate the water he requires in a dark place for a week or so, when the spores will die, or obtain his supply from a purer source. An investigation with a high po ver of the microscope of the turbid water complained of will 1 Views similar to my own have recently been expressed by Prof. Marsh and by G. K. Gilbert. speedily determine whether the explanation here suggested is the correct one. By way of illustration, I may mention that the water of the ornamental pond in the centre of the Horticultural Gardens, supplied clear and bright shortly before the opening of the Fisheries Exhibition, had assumed within a few days and still retains the colour and consistency of green-pea soup through the rapid development, under the action of light, of a unicellular cryptogam in the manner above described. W. SAVILLE Kent Singing, Speaking, and Stammering REFERRING to the letters in NATURE (vol. xxvii. p. 580) on my classification of vowel sounds, allow me to explain : The classifica ion given in the "Principles of Elocution" (4th ed., 1878) was retained from the earlier editions of that work, because of the difficulty, or impossibility, of exhibiting the complete vowel system of visible speech without V.S. symbols. For the purposes of the book on Elocution, the latter were not required; but a note (on p. 36) immediately preceding the "General Vowel Scheme " explains the basis of the complete classification developed in visible speech. As you have given an abstract of my classification, quoted by Dr. Stone from "Principles of Elocution," I shall be glad if you will show your readers the following abstract of the visible speech classification :— Classification of Vowels in Visible Speech Nine Lingual positions yield` 9 Primary vowels Each Primary vowel yields a "Wide" variety by faucal expansion=9 Wide vowels Each Lingual vowel yields "Round" variety by labial contraction a High Mid Low In this arrangement, each No. 1, No. 2, N. 3, &c., in the four sets is formed from one and the same lingual position. These relations are plainly exhibited in the symbols of visible speech. They cannot be shown by ordinary letters, but the use of numbers, as above, may make the arrangement clear to those who are not acquainted with visible speech. Washington, D.C., May 12 ALEX. MELVILLE BELL On the Cold in March, and Absence of Sunspots I WAS travelling when Dr. Woeikof's letter appeared in NATURE (vol. xxviii. p. 53), and could not sooner reply to his criticisms on my communication (vol. xxvii. p. 551), "Unprecedented Cold in the Riviera-Absence of Sunspots." Let me first remark that I do not go so far as to "ascribe (as Dr. Woeikof says that I do) the great cold of March, 1883, at the Riviera, to the absence of sunspots." My observations prove only the coincidence of a sudden and unprecedented visitation of cold, with an absence of sunspots (the more remarkable as occurring during a maximum sunspot period); and the further coincidence of a progressive rise in temperature with the return of the sunspots; but I add, "These observations are too few and too imperfect to warrant any decided conclusions; but they add to those already made in evidence of the connection between the absence of sunspots and the diminution of terrestrial heat; and I trust they may be followed by further and more exact investigations, to determine the influence of our great luminary on the weather and climate of the world." It does not appear to me that Dr. Woeikof has succeeded in establishing a parallel between Cannes and Suchum-Kale on the Black Sea; which, however sheltered locally, must, far more than Cannes, be liable to chilling influences in the cold winds from the lofty mountains and vast elevated steppes to the north, extending even to the Arctic regions. Therefore the fall of 31° below average in March, 1874, might not be extraordinary, even in a year with a considerable number of sunspots. It is not stated that the spots continued in this particular month. The case of Cannes may be thus stated: With a climate usually so mild in winter that frost and snow are of rare occurrence; and this winter, with slight frost only three times before February, and none at all in that month, the average minimum being 44°,-on March 7 minimum fell to 36°, with a heavy fall of snow; and on the 8th, 10th, 11th, and 12th, the minimum fell further to 27°7, 27°, 24° ́1, 25°·7. The sunspots, which had been observed by my friend, Mr. Campbell, of Islay, to be large and active until February 26, suddenly disappeared, and on February 28 and March 3 I found no spots; on the 10th and 11th only one or two small spots. On the 12th they began to appear in numbers, with a large oval facula. From that day they continued to increase, and the temperature gradually rose to the ordinary average. I will not occupy space with further arguments, but I will merely state some more facts with regard to the extraordinary intensity and universality of this invasion of cold, and my further observations of the sunspots. At my villa at Cannes, which is favourably placed in position and shelter, the register did not fall so low as in other parts. At Dr. Frank's villa, Grand Bois, more open to the north (thermometer in louvred box, a metre above ground), the minima were: March 7, 27°; 9, 25°2; 10, 21°; II, 21°; 12, 20°; 13, 25°. At Villa Beaulieu, more sheltered (therm. also in louvred box), minima were: March 7, 29°; 9, 27°; 10, 25°; 11, 26°; 12, 28°. Dr. de Valcourt's minima are somewhat higher; but he adds this note: "La période de froid du 7 au 14 Mars, 1883, a été très remarquable; elle est unique, depuis que les observations regulières ont été recueillis à Cannes." Where instrumental records are wanting, we refer to the report of the "oldest inhabitants," and learn that there has not been a cold so severe or destructive to oranges and olives since the year 1820. Extraordinary and intense as was this invasion of cold, it might have been supposed due to local or regional causes only, had it been confined to Cannes and its neighbourhood. In my former paper I stated that I was not informet how far the cold had extended to other countries and latitudes. We still need further exact information on this point, but what has already reached us goes far to prove that the cold was universal, and not limited to a region. In England, Mr. Thomas Plant writes to the Times from Moseley, Birmingham:-" After one of the mildest winters registered in the Midland Counties, the month of March, which is generally expected to be the beginning of spring, has been colder this year than any corresponding month for 38 years." "When we consider the power of the sun in March, as compared with December, January, and February, then we can reali-e some idea of the prolonged and most abnormal cold of the month now ended." By private information I learn that at the same time, in Stockholm, Centigrade's thermometer fell 13°, and at St. Petersburg 18°, below freezing. Unu ually intense cold in March is also reported from Canada. In the south we hear of snow and frost in South Italy, Sicily, Algeria, Egypt, and even Nubia. Later still there have been reports of snow on the mountains of Madeira and California, here it had never been seen before. Since March 19, the date of my former letter, I have been able to make sketches of the sun's position on 49 days.1 Of I use only a modest achromatic of 32 inches focus, and 2 inches aperture, which. projecting the solar image on a white card, exhibits the spots with umbra and penumbra, and the faculæ, sufficiently for this purpose. Of In these observations the following summary may suffice. number the spots varied from 3 to 18; the larger showing, more or less, holes or clefts of central umbra, with fringe of penumbra. Faculæ, or clouds of whiteness, were often seen around the larger spots. The spots varied in number and form from day to day; and although the same large spots and even groups could be traced for several successive days, they never retained the same aspect during the whole period of the sun's semi-rotation. On April 17 the spots were at their maximum; in number 18, in three groups. During this period, from March 19 to April 19-thirty-one days-the mean minimum temperature was 46° 2, mean maximum 57°9. From April 20 to May 7 there was considerable diminution of the spots; numbers not exceeding 8; and on May 7 there was only one large spot, with surrounding facula. The mean temperature of these seventeen days was-minimum 49°8, maximum 60°. From May 8 to 16 spots were few, from 2 to 8; but two of them were very large, with umbra and penumbra and sometimes adjoining faculæ. The mean temperature of these nine days was-minimum 52°7, maximum 63°*8. Here my observations terminate, as I left Cannes on the 16th, and have no means of observing in London, even if the atmosphere permitted. But I conclude by strongly commending the attentive study of the sun not only to astronomers and physicists, but also to practical meteorologists, as an interesting and not difficult addition to their work of observation, and one likely to supply information concerning the most important factor in the problems of weather and climate. C. J. B. WILLIAMS 47, Upper Brook Street, May 25 The Soaring of Birds My thanks are due to Mr. R. Courtenay for the notice he has taken (NATURE, vol. xxviii. p. 28) of my letter on the Soaring of Birds (vol. xxvii. p. 592). It is a great satisfaction to me to find my general conclusion supported by his observations. As to the possibility of a soaring bird utilising a downward current of air, I stand corrected. There is no difficulty in agreeing with Mr. Courtenay that the bird, finding itself in a downward current "will descend swiftly o as to acquire the necessary impetus for a rapid escape;"-that is to say, it will seek to make the best of a bad bargain. But it is not so easy to see that the bird, in a current approaching the perpendicular, will "acquire an impetus much more than compensating for the slight loss of elevation ;"—that is, will actually make a profit out of a seemingly adverse condition. This paradox, however, becomes more acceptable by the aid of an illustration:-A marble held lightly just within the rim of a hemispherical bowl, if let drop, will barely reach the opposite rim, but, if struck sharply downward, will run up the opposite side and leap up above the opposite rim. In like manner a bird, struck by a downward current as by a hammer-stroke, may speedily acquire a downward velocity greater than that due (under gravity) to the height through which it has descended; and may therefore rise, if it can escape from the downward current into a horizontal (or a fortiori into an upward) current, to a greater height than if it had fallen from the same startingpoint through still or horizontally-moving air. I am very much obliged to Mr. Courtenay for pointing out this interesting result. It gives completeness to the theorem, which now stands thus: that any alternations in the strength or direction of air-currents can be so utilised by birds as to enable them to soar. HUBERT AIRY Woodbridge, May 25 The Zodiacal Light THE phenomenon to which your correspondents allude, under the head of zodiacal light, was seen by me in the month of April, 1852. At the time I wrote a letter to the Times, in which I suggested it might be caused by the reflection of the sunlight at the surface of two masses of air of different densities, however irregular the bounding surface might be, in the same manner as the line of light seen reflected between the observer course a more powerful instrument would show a great deal more, both in number and in construction of the spots. For instance, on April 17, when I made out 18 spots, Mr. Campbell's solar image exhibited 104, with marvellous variety in the larger spots, and in the dome-like expansion of the adjoining faculæ. But these details, so deeply interesting in heliography, are not wanted for meteorological purposes. and the sun across the sea. One of your correspondents has suggested a more probable origin, viz. particles of ice in the air. From other correspondents it seems that the sun column is not always vertical, which might be the result of the general flame of the reflecting surface not being parallel with the earth's surface. In the June number of the Philosophical Magazine there was a notice of a sun column as seen at Orkney by the Rev. C. Clouston, who at that period made meteorological observations for that publication. He says that in the month of April of that year the drought was unprecedented, the atmospheric pressure great, and the temperature high. I believe two of these characteri tics belonged to the recent month of April if not the third, the high temperature. He says it was seen six times, and once or twice before he noted the date, and also before sunrise Saltburn, May 21 E. R. TURNER Sheet Lightning MAY not this be an auroral phenomenon, at times, at least, and hence the differences of opinion as to its nature? Reading Wilke's "Narrative of the U.S. Expedition," I find the folbowing:-"On the 7th February (1840) the weather had become less boisterous, and having reached latitude 49° S., longitude 155° 23 E., the aurora Australis again appeared. It was first seen in the north, and gradually spread its coruscations over the whole heavens; the rays and beams of light radiating from nearly all points of the horizon to the zenith, when their distinctive outlines were lost in a bright glow of light, which was encircled by successive flashes, resembling those of heat lightning on a summer's night. These formed a luminous arc in the southern sky, about 20° in altitude, from the upper part of which rays were continually flashing towards the zenith. Light showers of rain finally shut it out from view." FRED. PRATT Clapton Park, May 25 Pocky Clouds FOR twenty years I was constantly observing the forms and appearances of the clouds, as clues to the weather and its changes. I observed this form on a very great number of occasions, and from experience always came to the conclusion, "no rain today," and I can only remember two occasions on which the conclu-ion was not justified. I saw it again a few days ago, with the same result of good weather. I always termed it the "bubble" cloud till I saw Dr. Clouston's work. It seems to me to be a body of vapour the upper surface of which is being acted upon by an upper current of very dry and rarefied air, causing a great and rapid evapora tion, and thence a gradual and unequal cooling and shrinkage of the under surface in the de ached globules fron which it takes its ame. I have seen a very simple illustration while passing hrough the laundry, and observing a neglected trough of soapuds cooling down and nucleating in the exact form presented by the pocky cloud, and with the same gradations of tint. This kind of cloud is generally observable at periods most probable for storms and electric condensations, the which, acting at a distance, would influence outlying areas of upper atmophere and cause this form of cloud condensation in the way explained. In my observations I have generally found the cloud revert to uniform sheet stratus rather than to disappear in cloudlets in the upper air. FRED. PRATT Clapton Park, May 25 Clerk Maxwell's "Devil on Two Sticks" IN the very interesting life of Clerk Maxwell which has lately appeared there are frequent references to a philosophical toy, from which he seemed to derive endless amusement. He calls it the "devil on two sticks." Can you give your readers any account of it? The editors take it for granted that the apparatus is well known, but I cannot find any one here who can tell me what it is. DENNY LANE 72, South Mall, Cork The Centres of a Triangle CONTINUING my suggestion in your number of May 3 (p. 7), I propose not only to call the circle circumscribing a triangle the circumcircle, but also to call its centre the circumcentre, and in he same way to speak of the incentre, the three excentres (namely, the a-excentre, the b-excentre, and the c-excentre), and the midcentre. The line joining the circumcentre to the orthocentre, on which the misscentre and the mi centre lie, may be appropriately called the central line of the triangle. Similar abbreviations would apply to the radii of these circles; they might be spoken of as the circumradius, the inradius, the a-exra lius, the b-exradius, the c exradius, and the midradius. May 25 W. H. H. H. THE ROYAL GEOGRAPHICAL SOCIETY THE annual meeting of the Royal Geographical Society on Monday was of rather more than usual scientific interest. Sir Joseph Hooker was presented with the Royal Medal which the Society has awarded him, Mr. Colborne Baber being the recipient of the Patron's Medal; while among the speakers at the dinner, besides Sir Joseph Hooker, were Mr. Spottiswoode and Prof. Huxley. From the address of the President, Lord Aberdare, it is evident that geographical research, during the past year, yet, as the speakers we have named and especially exploration, has been as active as ever pointed out, the discovery of new countries must have a limit, and in time must come to an end. Still there will be plenty of work for geographers to do in the wider acceptation of the term geography, implied in the presentation of the Royal Medal to so distinguished a botanist as Sir Joseph Hooker. In the words of Mr. Spottiswoode, and as we have frequently pointed out in these pages, geography in its modern acceptation includes "an accurate delineation of the earth's surface, and an exact account of its inhabitants and of their habits, of the animal and vegetable life, and its distribution over the face of the globe." In this direction the Society has a long and brilliant career before it But as Prof. Huxley humorously pointed out in replying for the "other societies," these societies were all growing a little dull. He did not say this in the way of reproach. The progress made in research and accuracy in methods of procedure involved that consequence. So long as there were large regions of knowledge which the methods of modern science had not penetrated, so long was it possible to go to meetings of societies, and to hold brilliant discussions. Looking at the means which now existed for the diffusion of information, he had been led to think that in many cases where the field of knowledge had been extensively explored the utility of societies was constantly diminishing, and that sooner or later it would be necessary to devise other means of effecting the results now attained by meetings of societies. But there was one thing which would not be reached at any period of time by any other organisation than that of societies, and that was the stimulus which was given by their meetings to investigators; and the reward they found for their toils and sacrifices in such a welcome as had been given that night to his long-tried friend Sir J. Hooker." The prosperity of the society continues to be maintained. Mr. Clements Markham read the annual report, which showed that during the year the number of Fellows elected was 163, besides three honorary corresponding members, and the total number of Fellows on the list (exclusive of honorary members) was 3392. The total net income for the financial year ending December 31, 1882 (exclusive of balance in hand and 1005/. sale of Exchequer Bills) was 7937/., of which 56527. consisted of entrance fees and subscriptions. The net expenditure during the past year was 87797, including 11357. spent on expeditions. The sale of 1000l. of Exchequer Bills was rendered necessary to meet the Society's contribution to the Eira Relief Expedition, but this sum had since been generously presented to the Society by Mr. Leigh Smith. The investments and assets of the Society on December 31, 1882, exclusive of the map collection and library, amounted to 39,8311. THE TRUE ORBIT OF THE AURORAL METEOROID OF NOVEMBER 17, 1882 AF FTER many fruitless efforts to conciliate the apparently widely diverging data, given by the numerous observations of this most interesting phenomenon ; and after having been many times on the same point as Mr. H. D. Taylor (vol. xxvii. p. 434), who has given the first approximate calculations of this orbit, namely, “to give up the reconciling of such contradictory evidence," I have devoted my Easter holidays to new research on the true orbit. Besides the encouraging letters received from some of the English observers, I found still another motive in the observation of Mr. Julius Dupire at Laon (France, B 49° 34′), who had the kindness to give me ample information, for which I offer him my sincere thanks, and in the communication of the following citation, kindly given me by Prof. Ch. Muntigny, of Brussels, taken from the Bulletin de l'Obser = Data of observation. 87, 140, 434 The centre was 6° or 7° below the moon's centre (given not directly after observation); 30° elevation in meridian(probably a mistake or a printer's error, being in contradiction with the other data). 8° from Saturn, to the right, in a line inclined 45° to the horizon. First seen a lit le S. of Aldebaran; moves across the moon's disk. vatoire de Bruxelles, November 18, 1882: “À 6h. 23m. un énorme rayon d'un blanc vif s'éléva à l'horizon E.N.E.; il traversa le ciel en passant le zénith et alla s'éteindre à l'horizon O.S.O." A similar phenomenon has been observed by Dr. F. Terby at Louvain. The great attraction of the Laon observation consisted in the fact that the meteor's apparent path was there seen at the north side of the zenith, this being in harmony with the Brussels zenith observation, and promising a good determination of the sought orbit. In the first place I took the following apparent orbits from the numerous given observations. They can or must be taken as great circles, and must, in this case, fulfil the condition of intersecting one another in two opposite points of the sphere. In fact their intersections are contained within a small space and gave me an approximate position to one of these two points, a = 70° 30′, 8 = +14° 30'. These five apparent orbits, the only ones given completely, are the following: Tracing these five apparent orbits on a celestial globe they gave the intersection point above mentioned. It is clear that this point, joined with the eye of the observer, gives the direction of the true path. This point lying further, the globe being placed on the different latitudes and hours, not far from the point E. 20° N. of the eastern horizon (at Utrecht 7° above the horizon), it is evident that the lines of intersection, formed by the plane of the mean horizon with the planes of the apparent orbits must be nearly parallel to this direction. That these lines of intersection cannot be true parallels follows from the observations of the four students at Cooper's Hill (p. 97), from that of Mr. Joseph Clark at Street, communicated by Mr J. E. Clark, at York; and from that of Mr. A. S. P. at Cambridge (p. 87), who saw the phenomenon disappear in the S. W., S.W. and S.S.W. Further the Revue Mensuelle of M. C. Flammarion (2me Année, p. 72), containing a short report of Mr. Dupire's observation, mentioned above, gives also an observation made at Ploërmel (B = 47° 55', λ 2° 23′ W. Greenwich), where the phenomenon disappeared in the west. Now I have drawn a stereographic map on a large scale, and brought the intersection of the vertical plane through Brussels, with the bearing E. 20° N. It is clear that the true orbit must lie in the vertical plane. Further I have constructed the angles formed by the planes of the apparent orbits with the respective horizons, correcting, if necessary, for the curvature of the earth, and after much trouble found the following path, being a straight line having the properties given in the table on p. 106, that enables us at the same time to compare the results of my construction with the data of the different observations given in order from E. to W. I hope that the observers will be content with the degree of harmony between their observations and my results. I believe that a small change in the direction of the orbit's plane will give still more harmony between calculation and observation, but the orbit found satisfies the chief observed facts, and gives the greatest divergence, where the observations have the smallest sharpness. I believe I have proved by this research that there existed, with the aurora of November 17, 1882, cosmic dust, passing through the upper strata of our atmosphere with great velocity, and giving, according to the most interesting observation of Mr. Rand Capron (p. 84), "the usual green line" of the aurora spectrum. Thus nature itself has been so kind as to give an experiment that till now, and perhaps for ever, is beyond human IX. Lincoln's Inn 132 X. Cooper's Hill 130.6 W. 51° S. The centre 5° above the moon's A little above the About E.N.E., W.S.W. S.S. W., or W. 67° S. E.N.E., W. moon (p. 83). Across the face of the moon. Just below the S. 58° W. S. 45° W. moon. server. A. S. P. The inclination on the horizon, from observation 6° to 7°, from construction 7°. The altitude 62° uncertain, according to the From the Bulletin of the Observatory. The The maximum altitude seems to have been The eastern horizon cloudy, the width of the The angle below the moon's centre is given from It disappeared below the horizon in the P. 83. W. H. M. Messrs. Sykes, P. 99. Communicated by Mr. Herb. McLeod. John L. Dobson. P. 87. The apparent path not being very |