Mr. OUR ASTRONOMICAL COLUMN. EPHEMERIS FOR HALLEY'S COMET, 1909c.-A corrected ephemeris for Halley's comet is published by Crommelin in No. 4359 of the Astronomische Nachrichten (p. 249, September 28). This ephemeris, like that published in No. 4330 of the same journal, is based on the elements published, for the Astronomische Gesellschaft prize, under the pseudonym "Isti mirantur stellum," Messrs. Cowell and Crommelin, it transpires, being the calculators. The new observations do not yet cover sufficiently long arc to permit of an independent deter a the polar snows. For the newly discovered area in longitude 120° he proposes the name "Stella," suggested by its brilliant appearance. In the same journal M. Antoniadi records his observations, on September 19, of the Mer du Sablier, which to him appeared as Dawes recorded it in 1864. As Prof. Lowell's observations and photographs show it of a very different form during the period 1894-1907, M. Antoniadi suggests that periodic changes of form, probably irregular, may take place in this feature. A number of interesting observations of the planet are recorded in No. 22 of the Gazette Astronomique, by M. P. L. Dupont, of Hoboken, Antwerp. REMARKABLE METEORS.-No. 22 of the Gazette Astronomique contains the records of three remarkable meteors seen in Denmark during August. The first was at 9h. 25m. (C.E.T.) on August 19, and it was bright enough to illuminate the surrounding landscape. Apparently its actual path was from 128 km. above the town of Sorö, in Zealand, to 30 km. above a point on the coast about 22 km. west of Sorö; thus the path was nearly vertical, and the velocity was about 33 km. per second. The other two meteors were seen on the same night at 9h. 17m. and 9h. 38m. respectively. The former was attended by a noise similar to that made by escaping steam, whilst the second one was extraordinarily slow, and was seen for fifteen seconds, during which it passed, nearly horizontally, from 190°, +23° to 152°, +32°. THE URSA-MAJOR SYSTEM OF STARS.-Following up Dr. Ludendorff's conclusion that the stars B, y, d, e, and Ursa Majoris belong to a definite system of stars moving along parallel lines in space, Mr. Ejnar Hertzsprung has investigated the conditions for other stars having similar proper motions, and finds that a number of other stars probably belong to the same system. Among these may be noted B Auriga, Sirius, a Coronæ, 78 Ursa Majoris, and Groombridge 1930, while Boötis is suspected. A number of the stars, nine out of fifteen given, are double, and a tabulation of the magnitudes and spectral classes suggests a development of spectrum, from one star to another, with an attendant decrease of brightness (Astrophysical Journal, vol. xxx., No. 2, p. 135). SEARCH-EPHEMERIS FOR WINNECKE'S COMET.-A continuation of the search-ephemeris for Winnecke's comet is published by Herr C. Hillebrand in No. 4360 of the Astronomische Nachrichten. As the present southerly declination (-20°) is increasing, it is not likely that the comet will be generally observed in the northern hemisphere. THE NATURE OF SOLAR FACULE.-An important result concerning the nature of bright faculæ seen on the sun's disc is published by M. Deslandres in No. 11 of the Comptes rendus (p. 493, September 13). The main conclusion is that the vapours in the bright faculic areas are, relatively to the surrounding dark areas, descending. This result has been deduced from the measures of the motion-displacements shown on negatives taken with the Meudon spectro-register of radial velocities, the pure K, line being employed. Exhaustive measures of the absolute velocities have not been made, because to measure completely the whole disc on one negative would entail some 36,000 settings, and the Meudon staff is not sufficiently large for such an enterprise. But the measures of a number of displacements on bright areas near the centre of the disc, where the line-ofsight motions are independent of the solar rotation, indicate that the result is general. A diagram which accompanies the paper shows this result for a faculic area photographed on June 4. M. Deslandres discusses this result in comparison with atmospheric movements on the earth, and suggests that it is in accordance with theory. When a mass of vapour descends it becomes compressed, and therefore brighter: when ascending, its pressure is decreased, and consequently the vapour becomes cooled and less bright. The investigation of the nature of spots, on the same lines, has not yet been undertaken, M. Deslandres looking upon spots as a secondary phenomenon following the production of faculæ. PERCY SLADEN MEMORIAL EXPEDITION I. THE Percy Sladen Memorial Expedition was the outcome of a recent study of Welwitschia, that most remarkable of West African plants. Its primary object species characteristic of the dry, low-lying plateaux of Great Namaqualand were encountered for the first time. Prominent among these were Tamarix articulata, Aloe dichotoma, Statice scabra, Galenia articulata, Didelta annua, Exomis albicans, and Vogelia africana. This southern extension of the flora of tropical and subtropical Namaqualand seems to be confined to sheltered valleys at elevations not exceeding 2000 feet. 66 From O'okiep a detour to the northeast across the sandy plains of Bushmanland was rewarded by an unexpectedly rich collection, for unusually heavy rains had recently fallen. The plains were gay with the flowers of Hoodia Gordoni, Rhigozum sp., and a tall bushy Hermannia. A shrubby Aristida and some smaller species of the same genus were also very abundantly represented, while trees of Aloe dichotoma and large symmetrical bushes of species of Euphorbia were conspicuous on the kopjes." The natural vegetation along the banks of the Orange River forms a narrow belt, in which a distinct arrangement in subordinate zones can usually be traced. The lowest zone (Fig. 1) consists of a dense scrub of Salix capensis, Acacia horrida, Zizyphus mucronata, and a few other bushes, with some grasses, reeds, and sedges. Above the primary bank of the river the mountains rise steep, rugged and barren, or, between them and the stream, are stony flats (Fig. 1) all but devoid of vegetation. Having returned to O'okiep to refit, we arrived at Raman's Drift for the second time on January 22, and crossed to the German side on January 24. The river at this time was in flood, and its muddy waters were some FIG. 1.-A view across the Orange River near Raman's Drift, looking North. The river itself is concealed by the lowest zone of vegetation. was the investigation of the biology and morphology of Gnetum africanum, the only immediate relative of Welwitschia known to occur south of the Congo. It was further proposed to examine, so far as circumstances would allow, the flora of the desert-belt and of the regions adjacent to it. The expedition was under the auspices of the trustees of the Percy Sladen Memorial Fund, and was assisted by a grant of 200l. from the Royal Society. During the first section of the journey (Cape Town to Lüderitzbucht) I was fortunately able to travel in company with the magnetic survey expedition of the Carnegie Institute under my colleague, Dr. J. C. Beattie. A saving of half the ordinary cost of transport was thus effected. The route followed was very largely determined by the distribution of the usually widely separated water-holes. What would certainly have proved a very interesting part of the journey (viz. from Keetmanshoep to Windhuk) had to be abandoned owing to the necessity of arriving in central Angola before the end of the season in which suitable stages of the ovules of Gnetum were likely to be obtainable. Leaving Ceres Road Station on November 26 with a waggon drawn by twenty oxen, we ascended to the Ceres Plateau (1100 feet) through Mitchell's Pass in the Langeberge Range, and travelled for four days over an undulating tableland rising to 2500 feet, the flora of which is closely related to that of the mountainous districts of south-western Cape Colony. Unfortunately, most of this country was suffering from drought, and the botanical results were poor. At Karoo Poort we suddenly emerged upon the western tongue of the Karoo (November 30), which was crossed in six days. Here also the ground was parched; in some districts, it was stated, no rain had fallen for four years, and many of the farmers had migrated with their families and flocks into Bushmanland and other more favoured localities leaving their homesteads unoccupied. Over large areas all the non-succulent vegetation had disappeared and the flora consisted almost entirely of Augea capensis with a few species of Mesembrianthemum. Ascending the Blauwkrantz Pass in a spur of the Roggeveld Range on December 6, we came upon a plateau the flora of which is closely related to that of the Nieuveldt Mountains in the neighbourhood of Beaufort West. On December 10 a somewhat sudden descent to 600 yards wide at the drift. FIG. 2.-Great Namaqualand south of Warmbad, Aloe dichotoma, A few hours of heavy 1600 feet brought us again into a karoid region, in which travelling brought us upon a plateau (2300-4000 feet) where the vegetation proved to be richer than any hitherto met with. It was said that the rains which had fallen a few months earlier were more copious than any experienced during the previous fifteen or twenty years. It was no doubt a consequence of this that the annual constituents of the flora were unexpectedly abundant. Warmbad is noted for a number of warm springs (35° C.) the waters of which-like so many of the natural waters of the south-west coast-are impregnated with sulphuretted hydrogen. The railway between Keetmanshoep (3300 feet) and the sea ascends to nearly 5000 feet at Aus, where the vegetation presents many karoid features. From !Aus the descent-at first gradual, later more rapid-is uninterrupted. About 30 km. west of Aus (110 km. from the coast) the desert commences very abruptly at 2700 feet. In this latitude there appear to be few forms peculiar to the desert itself and its flora consists very largely of the more resistant of the species found at higher levels and under less arid conditions. Nevertheless, the eastern boundary of the desert is remarkably sharp, and approximately coincides with the western limit of precipitation from clouds condensed upon the neighbouring highlands. Within 50 km. of the sea the sharp, bare mountain peaks and ridges are frequently more or less buried in sand-dunes, the materials of which are blown up from the lower-lying flats, leaving behind the worn gravels from which diamonds are now being obtained over an extensive area. Nearer the coast the scenery is remarkably gaunt and rugged and the wind-swept surface is frequently quite bare of vegetation. Leaving Lüderitzbucht by sea on February 26, I arrived in Swakopmund eighteen hours later, and on March 2 reached Welwitsch (lat. 22°), a Welwitschia locality previously visited in 1907 in company with Mr. E. E. Galpin. The object of this visit was to obtain later stages of the Welwitschia embryo than were present in material collected in 1907. The flora in general was this year very much poorer than two years earlier. Not only were many of the smaller plants then collected not found at all, but woody species formerly obtained in flower or fruit now showed no signs of reproductive activity; this also applies to some extent to Welwitschia itself, for only a small proportion of the plants had coned. The explanation of this very striking difference seems to be contained in the meteorological records. Between 2 November 1, 1906, and January 31, 1907, 12.8 mm. of rain were measured at Welwitsch; in the corresponding period of 1908-9 the rainfall was 5.9 mm. In December, 1906, the fall was 12.5 mm., an amount very much in excess of that recorded for the whole of each of the years 1907 and 1908. We have here, then, another example of the remarkable influence of a small additional rainfall upon both the annual and perennial constituents of a desert flora. A large number of the Welwitschia plants present in 1907 in this easily accessible locality have been removed in the interval, and, at the same rate, a few years would probably have seen the complete disappearance of all plants from the vicinity of the railway, for there is here no sign of seed-reproduction. It is therefore very satisfactory to note that His Excellency the Acting Governor has issued instructions for the protection of the plants that remain. H. H. W. PEARSON. RESEARCHES ON THE ACTION CENTRES OF THE ATMOSPHERE.3 IN the domain of world meteorology, that is, the comparison and discussion of meteorological data of widely distributed stations over the earth's surface, Prof. H. Hildebrand Hildebrandsson has, during the last decade or so, been making some very important communications. He has clearly emphasised the fact that the laws which rule the general movements of our atmosphere will never be found if observations are only made in civilised countries on the earth's surface. Our atmosphere is a mass of air resting both on the continents and the oceans, and modern researches have shown that a large perturbation at one time in one area may be intimately associated with a perturbation of an opposite nature in the antipodal part of the world. Although several workers many years ago intimated the positions of isolated areas which behaved in a reverse or see-saw manner meteorologically, it was Prof. Hildebrandsson who first directed attention to a great number of such areas. In more recent times these isolated instances of barometric see-saws have been found to be part of really one general law applying to the movements of our atmosphere. This general law has yet to be more minutely investigated, for it is, as Prof. Hildebrandsson states, une verité avec des grandes modifications." There is little doubt, nevertheless, that world meteorology has made a considerable advance since the discovery of these simultaneous reverse-pressure changes, and one is now in a much better position to state where on the earth's surface observations should be made. Every attempt should therefore be made to utilise islands in the large oceans, even if the sole occupants of the islands are the meteorological observers themselves, for until the air movements over the oceans are carefully observed and recorded we shall still be left to a great extent in the dark. Prof. Hildebrandsson's most recent memoir deals chiefly with the northern latitudes of the northern hemisphere, and is devoted to a discussion of data with respect to the simultaneous compensation between types of seasons in different regions. The meteorological data here dealt with relate mainly to certain regions between the east coast of 1 NATURE, vol. lxxv., p. 536. 2 Meteorological observations at this station were commenced in November, 1906. 3 Kungl. Svenska Vetenskapsakademiens Handlingar, Band 45, No. 2. III. "Sur la Compensation entre les Types des Saisons simultanés en différentes Régions de la Terre." By H. Hildebrand Hildebrandsson. North America and Siberia, but some more southern stations are included. Without going into any great detail, the investigation may be summarised as follows. Prof. Hildebrandsson regards the state of the ice of the polar sea as being the principal cause of the different types of the seasons of different years. Thus a high summer temperature in the arctic sea to the north of Europe will set free a large amount of ice, and consequently the polar current arriving on the north coast of Iceland in February and March, and a branch of which, after skirting the east coast, is directed 'towards the North Sea, will bring much ice and will be surrounded by a layer of cold water. This current will cool the air in its neighbourhood. The result of the movement southward of these specially cold currents is that the land areas around the Arctic Circle and North Atlantic Ocean suffer successively from them by the lowering of their air temperatures. Prof. Hildebrandsson accompanies his statements with tables and an excellent series of curves, which are very convincing. He specially refers to the investigation of M. Peterson, who showed that a variation of 2° or 3° in the surface temperature of the sea is sufficient to create changes of considerable magnitude in the air temperature over very large areas. The main result of this research is to indicate that in certain cases a means is afforded of making forecasts for seasons. Thus, to take an example, he shows that, with two or three exceptions, in twenty-five years the temperature of the summer at the North Cape was in the following spring in opposition to that of Europe, represented by Debreezin. THE NATURE AND EXTENT OF AIR POLLUTION BY SMOKE.1 IN a former paper read at the Congress of the Sanitary Institute held at Leeds in 1897 an account was given of the quantity of soot suspended in and deposited from the atmosphere of Leeds. It was then shown that, on the average working day, 20 tons of soot are sent into the air of Leeds, of which half a ton falls on an area of four square miles, and of the latter from 20 lb. to 25 lb. stick, that is, are not removable by rain. The present paper contains a record of the atmospheric impurities carried down by rain and the effect of this rain water on vegetation. It also contains an inquiry into the diminution of daylight caused by suspended particles of soot. Ten representative stations were selected in Leeds and one at Garforth, about 7 miles due east of Leeds. The impurities, in the form of suspended matter, consist of soot, tar, sand, mineral substances, and, in solution, of sulphurous and sulphuric acids or their salts, chlorides, largely in the form of hydrochloric acid or common salt, and nitrogenous matter, in the form of nitrates or free and albuminoid ammonia. The results are embodied in the following table : ANALYSES OF RAIN WATER, LEEDS AND GARFORTH. The solid impurities were found to diminish rapidly in passing northwards from the centre of the town. Within the distance of a mile the quantity fell to less than half, and at 2 miles to less than one-fifth. The influence of the industrial centres upon the solid impurities stands out most conspicuously, as a glance at the table will show, i.e. in the chief industrial centres the solid impurities are roughly twenty times as great as in the purer atmosphere of Roundhay, about three miles north-east of the centre of the town (Fig. 1). The quantity is also determined by the prevailing winds, which are west, south-west, and north-east, and the drift of the impurities is consequently more towards the east than the west. Of the three constituents of the total suspended matter, the one which is least injurious is the mineral matter. This is abnormally high at the Leeds Forge, and consists principally of oxides of iron, lime, alumina, and silica, either escaping with the fumes from the furnace or thrown out mechanically. In a former series of experiments the amount of soot deposited was determined by collecting daily from a fresh surface a square yard of snow (which lay for several days), melting, filtering, and weighing the soot. The total deposit on the first day represented 16 cwt. to the square mile, and the daily increase was, on the average, 4 cwt. Taking a four-square-mile area covered by the town, and allowing for a diminishing fall on the fringe of the area, the amount carried down by the first fall of snow may be represented roughly by 10 cwt. to the square mile, and the daily increase as one quarter of this amount. Later results, as determined from the soot deposited with the rain water, are in close agreement with these figures. The analyses of the total deposit for the whole year show that at Hunslet (industrial centre) the soot amounts to 300 tons per square mile, at the Leeds Forge (industrial centre) to 250 tons, whereas at Woodhouse Moor (one mile north-west of the centre) it dropped to 80 tons. Taking the average of the stations which lie within the central four-square-mile area, we get 190 tons per square mile per year, or roughly half a ton per square mile per day. The amount of tar deposited with the soot was previously demonstrated by exposing glass plates I foot square at different points situated in and at distances from the town. These plates at intervals were washed under running water, and the residual deposit analysed. The amount of soot thus remaining, as determined from its carbon content, was found to be twenty-four times greater in the town than at a distance of nine miles. In the present experiments the tarry matter was estimated by extraction with ether. The quantity dropped from 80 lb. per acre per annum in the centre to 14 lb. per acre at a distance of three miles north-east of the town. The waste of fuel in the form of unburnt coal passing into the atmosphere is represented each year by about 300 tons per square mile in the centre of the town, or, over the whole area of four miles square, about 100 tons per square mile. The effect of these suspended impurities in diminishing the amount of sunlight in Leeds may be gathered from the fact that in 1907 the number of hours of bright sunshine was 1167 in the town, whilst four miles north-west it reached 1402 hours. The amount of daylight has also been recorded at two different periods by the quantity of iodine liberated from an acid solution of potassium iodide. On the first occasion, over a period of four winter months, it was shown that the smoke in an industrial centre absorbed one-quarter of the daylight as compared with a station one mile to the north-west. In the present investigation, carried out during the month of June of this year, the amount of daylight often fell to one-half in the centre of the town as compared with Garforth several miles away. The relation of soot deposit (black column) to daylight (light column) is shown in the diagram (Fig. 2). It is the tarry matter in the soot which causes the latter to adhere to and blacken buildings and vegetation. It is sometimes stated that it is the domestic smoke rather than industrial smoke which is injurious to plant life, on account of its higher content of tar. There is a certain justification for this statement, for the percentage of tarry matter in the total solid impurities is highest in the residential and lowest in the industrial areas, varying from 18 per cent. in the former to 4 per cent. in the latter. When, however, account is taken of the total tarry matter deposited each year, the industrial centres are responsible for the greater quantity, which reaches in some cases ten times the amount in the residential districts. The total sulphur, either as sulphurous or sulphuric acid, is everywhere high, but particularly in and near the chief manufacturing arcas. A large portion of the free acids is neutralised either by the alkaline fumes of the blast furnaces or by the ammonia of the burnt coal. Still, free acid is present in considerable quantity, and in Hunslet (industrial centre). represents an annual deposit of 90 lb. per acre, or 25-30 tons per square mile. It is the sulphurous acid which imparts to town fog its choky and irritating effects. The large amount of this acid present in fogs may be gauged from the fact that the hoar-frost collected during the dense fog of January 27 contained acid corresponding to 10-29 parts per 100,000, or more than ten times the average acidity of the same station. To demonstrate the detrimental effect of sulphuric acid upon vegetation, Timothy grass was sown on May 12, 1908, in boxes 1 foot square, the soil being uniform. The seed was watered at a rate corresponding to the average rainfall of 25 inches with water containing different amounts of sulphuric acid. In addition to this, three other samples were watered with Garforth rain water in which the acidity was neutralised, the second with ordinary Garforth rain water, and the third with Leeds rain water. The results were very instructive. In the case of Leeds rain water and of those waters containing a higher degree of acidity, germination was distinctly checked, and the delicate green of the young grass quickly changed to yellow or brown. Grasses watered with water containing, 32 parts per 100,000 were killed in a little more than three months, and with 16 parts per 100,000 in less than a year. Chlorides are found in large quantities, especially in the industrial centres, where, expressed as common salt, they sometimes reach as much as 3 or 4 cwt. per acre, a quantity which must be distinctly prejudicial to vegetation. The nitrogenous impurities, on the other hand, would be beneficial by acting either as direct stimulants and fertilisers or by neutralising the acidity of the sulphur and chlorine compounds. MATHEMATICS AND PHYSICS AT THE THE proceedings of Section A began on Thursday, A paper followed, by Prof. J. H. Poynting and Mr. Guy Barlow, on the pressure of radiation against the source. The authors employ thin slips of material which become heated by incident radiation. Those black on both sides experience a pressure equal to the energydensity, P, of the incident radiation; those black on the incident side and brightly silvered on the other experience a pressure 1.67 times as great, the excess being due to the radiation which is emitted by one side only of the plate. Plates which are bright both sides experience a pressure 2P, because they do not become heated. Experiments, which are in progress, give good accord with theory. In a short discussion which followed, Prof. Hull intimated that he was alive to the possibility of this reaction when making his experiments on the pressure of incident radiation, but his experiments had been devised carefully so as to prevent its occurrence. Prof. T. Lyman then gave a summary of the ascertained properties of light of very short wave-lengths ("Schumann rays"), including their ionising and photoelectric effects. To these Prof. Bumstead added that one of his students had shown that the velocity of the electrons emitted photoelectrically increases directly as the frequency of the light up to a wave-length A= 1250-a result which Ladenburg had previously shown to hold good for ordinary light. Prof. Percival Lowell followed with an account of the photographs of Jupiter taken at the Lowell Observatory. The slides exhibited showed a wonderful amount of detail, the most noteworthy features being faint wisps that crisscross the several belts, particularly the bright equatorial one. He explained the belts and wisos as gaps in the clouds formed by condensing of uprising vapours from Jupiter's heated interior (he being still a semi-sun), and strung out by his rotation. Prof. Larmor added greatly to the interest of the paper by exhibiting some early drawings of Jupiter made by Sir W. Huggins, and stated that Sir William's opinion from the first was that the wisps were the edges of cumulus clouds. He noted that the high albedo of Jupiter (72) indicates that the Jovian atmosphere acts like a bright cloud; it follows that very little of the meteorology of Jupiter can be due to the sun if heat is only absorbed like light. Other planets with a low albedo would have surface markings more like terrestrial ones. The day's proceedings concluded with a paper, by Prof. E. E. Barnard (read by Prof. E. W. Brown). on the motion of some of the small stars in Messier 92 (Herculis). Two of the stars in this cluster are shown to have proper motion; the first (No. 11 of Schultz's list) is moving away |