66

labours of the anatomist and the museum-worker. "What engineer," writes the Professor, I can be said to understand his business if he knows not the purpose to which the machines he makes are to be applied, and is unacquainted with their mode of working. We may investigate thoroughly the organs of any animal, we may trace them from the earliest moment in which they become defined, and watch them as they develop to maturity, we may comprehend the way in which every part of a complicated structure is built up; but if we take not the trouble to know their effects on the economy of the creature, we as naturalists have done but half our task, and abandon our labour when the fulness of reward is coming upon us." All honour then to those (if only they work in the right way) who risk their health, if not their lives, and spend their treasure, in the quest of the rarer birds' eggs!

Although they have been removed from the list of desiderata, the eggs of the curlew-sandpiper will probably long remain among the rarest of those of the British species, those from the Yenisei being the only specimens at present known. Among the species included in the British lists whose eggs were unknown at least as late as 1896, is Pallas's grey shrike (Lanius sibiricus), but as this bird is so closely allied to the ordinary species, their discovery cannot be looked for ward to with any special interest. The second is the needle-tailed swift (Chatura caudacuta), which has only twice been seen in Britain, and breeds in northern Asia, although its eggs are still unknown. Equally slight are the claims of the sharp-tailed sandpiper (Tringa acuminuta) to be regarded as British; and, although still unknown, its eggs will probably prove very similar to those of the American T. maculata. To the rare and beautiful wedge-tailed gull (Rhodostethia rosea), reported to have been once seen in Britain, is provisionally assigned a single egg in the British Museum obtained from Disco Bay. Of far more interest would be the discovery of the eggs of the Cape petrel (Daption capensis), since this bird, of which an example was killed in Dublin in 1881, represents a genus by itself. One of its breeding-places appears to be Kerguelen Island. Of two other petrels, namely Estrelata hæsitata and E. brevipes, with equally slight claims to admission in the British lists, the eggs are likewise unknown.

Of species whose eggs are known, although of extreme rarity, next to the curlew-sandpiper, the white-billed diver (Colymbus adamsi), a by no means very rare visitor to our coasts, may first claim attention. The only known eggs, which are very like those of the great northern diver, were obtained during the voyage of the Vega in 1879. Of the lovely ivory gull (Pagophila eburnea) the eggs have been described by Prof. Collett; while those of the Iceland gull (Larus leucopterus) and Mediterranean black-backed gull (L. melanocephalus) come also under the category of rarities, the nest of the latter species being unknown. Of greater interest are the beautiful eggs of the Sandwich tern, of which additional specimens were recorded last year. Although obtained by Wolley, the eggs of the spotted redshank (Totanus fuscus) must be regarded as prizes by the collector; while so late as 1893 those of the solitary sandpiper (T. solitarius) were recorded by Mr. Dixon as unknown, although one clutch has been described by Mr. Elliot, in which the eggs resembled those of the piping sand-plover. Claim to a place in this section is undoubtedly held by the sanderling, of which eggs were obtained by MacFarlane in Arctic America in 1863, and subsequently by Colonel Feilden in Grinnell-land. The knot (Tringa canutus) is another of the species which appears in Mr. Dixon's book of 1893 as among those of which the eggs are unknown. It seems, however, that a clutch of four was taken in Greenland as far back as 1875, one of which is now in the British Museum; and these, with a

single specimen taken from the body of a female by Lieut. Greeley, appear to be the only examples in collections. Far less uncommon are the eggs of the little stint (T. minuta), although they still come under the category of rarities, as do those of the jack snipe, which were first taken by Wolley in Lapland. The crestless lapwing (Vanellus gregarius), of which but one British specimen is on record, is also a bird of whose nidification details are wanting, although the eggs are known to be four in number, and very similar to those of the crested species. Dotterel eggs, although very handsome, can now scarcely be considered as rarities; but those of the lesser golden plover (Charadrius dominicus) are very scarce, although their similarity to those of the ordinary species renders them less interesting than would otherwise be the case.

Passing other members of the foregoing groups whose eggs are more or less scarce, allusion must specially be made to the common bernicle goose, of which it is a remarkable fact that eggs laid in a wild state are quite unknown, although this is somewhat discounted by the circumstance that birds have nested in captivity. Of the nearly allied red-breasted bernicle (Bernicla ruficollis) the eggs have, however, been discovered, and, except for their somewhat smaller dimensions, are stated to be indistinguishable from those of the bean-goose.

Although the eggs of all the species of birds of prey recorded as British are known, some are comparatively rare in collections. Among such may be mentioned those of the red-footed kestrel (Falco vespertinus), which although not uncommonly taken in Russia, were so poorly represented in the British Museum in 1896 that Dr. Bowdler Sharpe stated he was unable to properly define their characters.

In addition to those of Pallas's shrike, which have already been mentioned in the unknown list, the following are some of the rarer eggs among the British Passerines. From their beautiful markings the eggs of all the buntings are always favourites with collectors; and from their rarity those of the rustic bunting must be specially prized. Two only are in the Seebohm collection in the British Museum, although others have been described by Mr. Dresser, and yet others are mentioned by Prof. Newton as among the specialities of last year's collecting. Richard's pipit (Anthus richardi) affords an example of a bird of which the eggs are known, but the nest has never been described. Among comparative rarities the eggs of the yellow-browed willow-warbler (Phylloscopus superciliaris) and the marsh-warbler ( Acrocephalus palustris) deserve passing mention, especially as many referred to the latter species appear to be nothing more than pale examples of the reed-warbler., Perhaps the greatest prizes among the British representatives of the group are, however, the eggs of White's thrush (Turdus varius). A nest, with eggs, from Ningpo attributed to this species is included in the Seebohm collection, and undoubted specimens are mentioned in Prof. Newton's list of new acquisitions. Less rare are the eggs of the black-throated ouzel (T. atrigularis), of which several clutches have been taken in the Altai, although the nest is still unknown. Another desideratum is the nest of the Siberian ground-thrush (T. sibiricus), of the eggs of which three specimens taken in Japan, and now in the Seebohm collection, were the only examples known up to 1896. Of the Arctic bluethroat (Cyanecula suecica) the eggs, which resemble those of a redwing in miniature, are far less rare, but must still be reckoned as among the collector's choicest treasures.

To go further into the British list would be beyond the limits of this article, while, as already said, species not occurring in that list must be excluded. An exception may, however, be made in favour of the rare Pander's chough-thrush (Podoces panderi), of the deserts of Central

Asia. Of this bird the eggs were first obtained, we believe, by Fedtchenko, and have ever since ranked as great rarities, and collectors will therefore be interested in finding specimens included among those collected last year and mentioned by Prof. Newton. R. L.

NOTES.

THE Council of the Royal Society have invited Dr. Wilhelm Pfeffer, professor of botany in the University of Leipzig, and foreign member of the Royal Society, to deliver the Croonian Lecture on March 17. The subject of the lecture is to be "On the Nature and Significance of Functional Metabolism (Betriebsstoffwechsels) in the Plant." The lecture will be delivered in German. Prof. Pfeffer is well known among botanists for his two volumes on "Pflanzenphysiologie," published in 1881 from Tübingen, and the second edition of which was issued last year ; while his views on the function of chlorophyll, and its absorptionspectrum, are familiar to workers on the physiology of plant

life.

MORE than 100 foreign zoologists have now consented to be members of the "Committee of Patronage" of the Fourth International Congress of Zoology, and a large number of them have expressed the hope that they will be able to be present at the meeting in August next. Among these we may mention the names of Prof. Häckel, of Jena; Prof. Graff, of Graz; Prof. Grassi, of Rome; M. Blanchard, of Paris; Baron Jules de Guerne, who has been associated with the Prince of Monaco; Dr. Jentink, of Leyden, who was President of the Third Congress; Dr. Dollo, of Brussels; and Prof. Collett, of Christiania. From the United States it is hoped there will be a somewhat large contingent; Profs. Osborn and Scott, Prof. E. B. Wilson, and Mr. Watasé, of Chicago, all hope to be able to

come.

THE sixth "James Forrest" Lecture of the Institution of Civil Engineers will be delivered on Thursday, March 17, at

eight o'clock. Prof. W. Boyd Dawkins, F.R.S., the lecturer, takes for his subject "Geology in relation to Engineering."

THE Mayor of Bradford presided at a meeting, held on Monday, for the purpose of considering a proposal to invite the British Association to Bradford for the year 1900. It was unanimously decided to send an invitation to the Association for the year 1900, and an executive committee was appointed to make arrangements if the invitation should be accepted.

IT is expected that some of the observers of the recent total eclipse of the sun will give a preliminary account of their observations at the meeting of the Royal Astronomical Society

to-morrow.

THE Municipal Council of Paris have inserted in the budget for this year the sum of ten thousand francs, for the laboratory of photography and radiography at the Salpêtrière.

THE following grants have recently been made by the Trustees of the Elizabeth Thompson Science Fund:-250 dollars to Prof. Gustav Hüfner (Tübingen), for the investigation

of hæmin and hæmatine; 288 dollars to Prof. Carlo Bonacini (Modena), for researches in colour photography; 250 dollars to Prof. John Milne, to aid in a seismic survey of the world.

THE Zürich correspondent of the Times states that the observatory on Mont Blanc, which was constructed by M. Joseph Vallot some seven years ago, is to be transferred to another site. The present structure is built on a small rocky plateau, which extends for a short distance from the Rochers des Bosses, but its position is no longer favourable for scientific observations. The construction of the building has served as a

barrier against which the snow piles itself in ever-increasing masses, causing both trouble and expense to the observatory staff. The whole erection is to be transferred, piece by piece,

on the backs of workmen from the Rochers des Bosses to a rocky point at the same altitude, where the ground will first be levelled by blasting, and, in spite of the difficulties of climate and transport attending these operations, it is hoped that the whole transfer will be finished in the course of one summer season.

AT the meeting of the Entomological Society of London on March 2, a discussion took place on the reported introduction of the San José scale, Aspidiotus perniciosus, into Great Britain. Mr. R. Newstead, the only British entomologist who is now specially occupied with Coccidæ, stated that during the past nine years he had never once met with this species among the numerous scale-insects taken in this country and forwarded to him for identification. It was impossible even for an expert to distinguish it, without careful microscopical preparation and examination, from among the thirty or more described species of Aspidiotus, and any attempt to identify it on imported fruit by naked-eye observation, or with a hand-lens, was therefore quite impracticable. The risk of its distribution by importation on fruit was small; there was, however, much more likelihood of its introduction on plants or trees. At the same time he saw no reason to suppose that it would be more injurious in this country than the common Mytilaspis pomorum; in America the San José scale had several, sometimes as many as five, generations in the year, but in this climate it would probably conform with the habits of all other scale-insects at present investigated and become single-brooded. Mr. Newstead's conclusions were generally agreed with by the Fellows present.

ACCORDING to the Bulletin de la Société Française de Physique, M. Crémieu has devised an ingenious means of producing elliptic sound-vibrations in air. By the interference of the longitudinal vibrations of two organ-pipes, placed at right angles, and vibrating under the influence of two diapasons with the proper difference of phase, an elliptic motion was set up at the intersection of the tubes, and its existence was made evident by means of delicate quartz fibres which followed all the move. ments of the air.

M. A. LEDUC, in a paper read before the Société Française de Physique, criticises the well-known law of mixture of gases, according to which the pressure of a mixture is the sum of the pressures of its constituents at the same volume and temperaThis law is only true for perfect gases, and is then equivalent to the statement that the volume of the mixture equals the sum of the volumes of its constituents at the same pressure and temperature. From experiments on several gas-mixtures, M. Leduc considers that the second form of the law is

ture.

rigorously applicable to certain mixtures of real gases, and is, in general, in closer approximation with experiment than the first.

IN the Annales du Bureau Central Meteorologique, M. Moureaux gives an account of the different comparisons he has made between the magnetic instruments of the Parc Saint Maur Observatory and those of the observatories at Kew, Uccle (Brussels) and Pavlovsk (St. Petersbourg). The comparison observations made at Kew have already been described by Mr. Chree in a communication to the Royal Society. The declination at Pavlovsk was found to be 1'3 higher than the French standard, the horizontal force 0'00013 lower, and the dip o'8 lower. At Uccle the declination was 1'5 lower, the horizontal force 0'00002 lower, and the dip was not compared. In the account of the Kew comparisons an arithmetical error occurs which makes the horizontal force difference 0.00011 when it ought to be o'00012.

IN connection with recent measurements of the temperature of the air at high altitudes, Signor Luigi de Marchi, writing in the Rendiconto del R. Istituto Lombardo, discusses the validity of Mendeléefs and Herschel's laws connecting temperature with altitude, and draws conclusions which may be briefly summed up thus:-(a) Recent measurements of temperature of the higher strata of the atmosphere can be represented by a formula of the type of Mendeléef's, viz. t + C = (T + C) p/P, where, however, C. increases with the altitude; (b) for altitudes below about 4500 metres the formula agrees with observ. ation when C is taken as a linear function of the altitude, but for greater altitudes, up to 13,000 metres, the supposition that C is a linear function of the pressure gives the best results, the formula then reducing, like Herschel's, to an equation of the second degree in p; (c) for altitudes of a few thousand metres Mendeléef's formula gives sufficiently approximate results when C is taken to be constant; (d) the validity of the proposed formula, if substantiated by further observations, would confirm the hypothesis that the temperature of a stratum at any given altitude is determined principally by the equilibrium between the thermal radiations which it receives from the ground, and which it emits into the sky, when the assumed law of radiation is that of Newton or of Stefan. The latter law in the strata hitherto reached would lead to a formula less reconcilable with the data of observation than the former.

ONE of the difficulties which water-engineers have to face is the unpleasant odour which sometimes characterises surface waters stored in open reservoirs. Such odours are frequently supposed to be due to the decomposition of organic matter in the water, but, although such may be the case, in many instances they have been found to be attributable to the growth of microscopical organisms, and quite a long list has now been furnished of vegetable growths which impart disagreeable tastes

grassy smell.

and smells to water. Messrs. Jackson and Ellms have just published a memoir describing their investigations upon one of the Cyanophycea or blue-green Algae which, when growing in water, impregnates the latter with a most unpleasant mouldy Pure cultures of Anabena circinalis, an important offender in this particular, were obtained and numerous experiments were carried out. As in the case of other microscopical water-organisms, the odour emitted during growth was found to be due to the presence of certain compounds of the nature of essential oils which make their appearance at a particular stage of growth. The investigation was also extended to an examination of these Anabæna during decay, a most offensive odour being given off during decomposition. This the writers think is probably due to the high percentages of nitrogen which these growths contain. The gas given off during decomposition was analysed and was found to contain a large percentage of hydrogen, and a considerable proportion of sulphur compounds. Analyses of the decayed gelatinous material resulting from the decomposition of Anabæna revealed the presence of a large amount of sulphur and a considerable amount of phosphorus. The subject is of such importance in connection with the storage of surface waters, that the closer study of the chemical composition of these organisms and of the organic and mineral contents of the waters which the various genera infest, is well worthy of attention; for by extending our knowledge in this manner, we should be better able to judge beforehand of the likelihood of particular waters becoming subject to these unpleasant changes on storage. The above memoir is to be found in vol. x. of the Technology Quarterly, Massachusetts.

THE receipt by the University of Pennsylvania of a collection of mammalian fossils from the tundra at the back of Point Barrow, Alaska, has induced Mr. S. N. Rhoads to put together

the available information on the living and extinct species of North American Boves. Mr. Rhoads refers one of the Alaskan Bison-heads to an unnamed species which he proposes to call Bison alaskensis (Proc. Ac. N.S. Phil., 1897, p. 490). He has likewise taken this opportunity to examine the question of the so-called "Woodland Bison" of the Peace-River district of Athabasca. It appears that an adult male specimen of this little-known animal has recently been obtained by the Geological Museum of Ottawa. Mr. Rhoads describes this example from information sent to him by Prof. J. Macoun, and refers it to a new sub-species, Bison bison athabasca, separating it from the typical form on jaccount of its "great size, darkness of colour, and the characters of the horns and horn-cores."

AN interesting article on the wild cattle of Chartley, Staffordshire, is contributed to Nature Notes by Mr. J. R. B. Masefield. This herd of wild white cattle is of great antiquity; but whether the present animals are directly descended from some one of the ancient native species, such as Bos primigenius, Bos longifrons, &c., or whether they are descendants of domestic cattle introduced by the Romans and run wild, is still an undecided question. The home of these cattle is situated on high ground some 300 feet above sea-level, and was enclosed about the year 1200, and forms a portion of Chartley Park, some five miles from Uttoxeter, the nearest town. The extent of this wild tract of table-land is about 1000 acres, covered with coarse grass, rushes, stunted bilberries, and heather, and patches of luxuriant bracken fern, with a few clumps of old weather-beaten Scotch firs and birch, which afford some shade from the hot summer sun. Among the other denizens of this wild primeval tract are herds of red and fallow deer and multitudes of rabbits, (with no doubt a few of their natural enemies, the stoat and voles-both the common vole and red bank vole), moles, long-tailed field mice, shrews, weasels, and adders. The theory that the Chartley breed of wild cattle is indigenous appears to be supported by their general habits at the present day. When alarmed they start off at full gallop for a short distance, then

turn and face their foe in a semicircle, with the bulls in front, the cows behind, and the younger animals and calves still further in the rear. If closer approached, these tactics, which are clearly those of wild animals, are repeated, or the adversary is charged and attacked. Again, they conceal their young in fern or long rushes, and the cows, when calves are born, become exceedingly fierce and dangerous, especially if an intruder should get between a cow and her calf. Mr. Masefield points out that a fine herd of white cattle, very strongly resembling the Chartley breed, are to be found at Lamphey Court, near Tenby, in South Wales; they are said to belong to an old Welsh breed, but in colour and general appearance it is difficult to distinguish them from the Chartley animals.

M. P. VUILLOT has completed a map of the lake districts of Timbuktu on the scale of 1/100,000, which contains a number

of topographical discoveries in this little-known region. In presenting the map to the Paris Geographical Society, M. Vuillot adds an interesting note on the hydrography of the area, and on its productiveness, which has been published in the Society's Comptes rendus.

PROF. THEOBALD FISCHER contributes a short paper to Petermann's Mittheilungen on the "moraine-amphitheatre" of the Lake of Garda. The form of the moraine deposits on the inner or Italian side of the Alps differs markedly in type from that on the outer or German side. In the former type, of which the Lake of Garda affords an excellent example, the deposits are laid down in concentric ramparts which turn their convex side to the plains; while in the latter we find the familiar expanded fan shape at the mouths of the valleys. Dr. Fischer avails himself of the very excellent maps and models furnished by the Italian Service.

THE first two numbers of the new volume of the Mittheilungen of the Vienna Geographical Society are devoted to a memoir on he Hallstätter See, by Dr. Lorenz, Ritter von Liburnau, which extends to over 200 octavo pages. The form and position of the lake are discussed, chemical analyses are given of its waters and of the waters of the inflowing streams, and there are elaborate investigations into the distribution of temperature at different depths and at different seasons, into currents, transparency and colour of water, and the various forms of life. Dr. Lorenz had the assistance of a large number of colleagues in making his observations, and was fortunate in having a steam launch placed at his disposal free of cost.

Petermann's Mittheilungen contains an account of a recent expedition into the interior of Dutch East Borneo by Dr. A. W. Nieuwenhuis. The region between the upper basins of the Kapuas and the Kutei or Mahakam rivers was not visited by the Dutch expedition of 1894, owing to the supposed hostility of the natives; but by judicious treatment and selection of native companions, Dr. Nieuwenhuis has succeeded in exploring a considerable area. A stay of eight months was made at a station on the Bloeoe, a small right-bank tributary of the Mahakam, giving opportunity for detailed topographical and geological surveys. Extensive collections were made, which have reached Buitenzorg in safety.

In descending the Niger, the Hourst Expedition found the navigation of that river impeded by rapids from Ansongo to below Boussa. As this was during the season of high water, M. le Lieut. de Chevigne was detailed in May 1897 to make a further reconnaissance when the river was at its lowest. The results of his observations are published in the Comptes rendus of the Paris Geographical Society, and are described as of special importance on account of a French station having been recently established at Say. The Niger is to be considered as navigable from Timbuktu to Ansongo, but only during high water; below Ansongo, rocky shallows and rapids render navigation difficult at all seasons, and dangerous, if not impossible, for nine months in the year.

IN the Bulletin of the Imperial Society of Naturalists of Moscow, No. 2 for 1897, is a lengthy and important paper (in German) by C. Sokolowa, on the growth of root-hairs and rhizoids. He appears to have come to the conclusion that neither the growth of the cell-wall nor the currents in the protoplasm are directly dependent on the cell-nucleus, although the position of the nucleus appears to a certain extent to determine the direction of the currents. N. Mali scheff contributes some remarks on the nerve-endings in the sophagus and stomach of birds. The remaining papers are

in Russian.

DR. F. VON KERNER publishes a short account of some recent geological work on the coast regions of Dalmatia in the Verhandlungen of the Austrian Geological Survey. The peninsula of Ostrica, the island of Zlarin, and a number of the neighbour ing rocky islets were surveyed, disclosing some features of geological and geographical interest. The islands together form part of the submerged lower course of the river Kerka.

AT the recent Ithaca meeting, the Association of American Anatomists adopted the report of the majority of the Committee on Anatomical Nomenclature, and ordered it to be published and distributed as soon as practicable, accompanied by the objections of the minority of the Committee, and comments thereon by the Secretary of the Committee. Of the neural terms recommended, more than 100 were identical with those adopted in 1895 by the Anatomische Gesellschaft.

WITH reference to our note on M. J. Deniker' papers on the characteristics of the inhabitants of the various districts o Europe (p. 351-2), the author writes to correct an error which

unfortunately crept into his paper. In our note, p. 352, line 14, the race "(8) Blond, mesocephalic, very short," should be ascribed to Saxony-Poland instead of Sweden.

THE additions to the Zoological Society's Gardens during the past week include a Masked Paradoxure (Paradoxure larratus), a Large Indian Civet ( Viverra zibetha) from Western Szechuen, China, presented by Mr. Julius Newmann; three Punjaub Wild Sheep (Ovis vignei, & 99) from Southern Persia, deposited; a Common Seal (Shoca vitulina) from Holland, an Indian River Snake (Tropidonotus piscator) from India, purchased; a Leopard (Felis pardus), born in the Gardens.

OUR ASTRONOMICAL COLUMN. OCCULTATION OF ANTARES.-The occultation of a star of the first magnitude is of rare occurrence, more especially when the moon is at such a favourable age as in the case of the occultation of Antares (a Scorpii) magnitude I'I, on March 13, when the moon is in the last quarter. The times of disappearance at the bright edge and reappearance at the dark edge, as given in the Nautical Almanac, for Greenwich are 14h. 38m. os., and 15h. 49m. os; and the angles at which these respective phenomena take place are 111° and 305°, measured from the vertex. The occultation of this beautiful red star is a most interesting observ ation, especially at the favourable phase of the moon, which should render the doubling of Antares easily visible. It was during an occultation that Burg discovered the celebrated blue companion in 1819.

NAUTICAL ALMANAC, 1901.-The Nautical Almanac for the year 1901 has just been issued. It is arranged in a similar way to those now familiar to us, and from it we learn the details of the total eclipse of the sun which takes place in that year on May 17. The path of the shadow passes over Sumatra, Borneo, Celebes, and the southern part of New Guinea; the eclipse will also be visible in Australia, but only as a large partial one, whilst in Europe and America no trace of it can be observed. This eclipse is remarkable for being one in which the duration of totality is nearly the longest possible, the maximum obscuration of the sun lasting about six and a half minutes.

We notice also that in accordance with the decision of the Paris Conference on Fundamental Stars, held in May 1896, the constants of precession, nutation, aberration and solar parallax, as set forth at that meeting, have been adopted. The new value for the solar parallax is, therefore, 8" 80 instead of 8" 848, and this is probably correct to within o''02.

Part I. of the Almanac is issued separately, as of late years, and contains such information as is essential to navigators.

VARIABLE STAR U PEGASI.—In a recent issue of NATURE, p. 352, we noted Mr. O. C. Wendell's observations of the short-period variable, made at the Harvard College Observatory, and the results of which were issued by Prof. Pickering in Circular No. 23. In the Astronomical Journal, No. 426, Mr. Chandler brings data together to show that the light curve is, as was originally laid down, of single period, and not analogous to that of B Lyra, with a small difference of o 15 mag. between the primary and secondary minima. He also points out that the polarising photometer failed to make manifest the secondary minimum of the star Z Herculis, a phenomenon involving a difference of nearly o'5 mag., or three times the amount in

question.

In Circular No. 25 (on polarising photometers), Prof. Pickering points out that the objections to the first form of photometer have been remedied, and now the emergent pencils of the images compared coincide, and a surprising degree of accuracy may be obtained in the measures, which is illustrated by numbers from actual observations. He also gives the individual results derived from Mr. Wendell's observations, and these show that the largest value of the secondary minimum is 0 05 mag, less than the smallest value of the primary minimum. Besides this he shows that if the minima be assumed to be equal, the residuals at first minimum have a mean value of +0*064, and at the second the mean value is 0070. He concludes that "the probability, therefore, that the two minima are really equal and that these deviations are due to accidental error is extremely small; and it is very singular that if these deviations are due to systematic error, that it has one value at principal minimum and another at secondary minimum."

THE PHOTOGRAPHY OF NEBULE.

PHOTOGRAPHY has been a helpful handmaid in many branches of astronomical science, but in no department is the value of her assistance more clearly seen than in that which is concerned with the forms and structures of nebulæ. This is hardly to be wondered at when the fine texture, the almost imperceptible gradations of light, the intricacy of detail, and the variety of nebulous forms are considered. Many vigils must be kept by an astronomer before the trend and comparative distinctness of a particular nebulous feature is satisfactorily observed; and even where this has been done, to represent the characteristic faithfully is beyond the power of any but the most accomplished draughtsmen. The unimaginative photographic plate, however, looks heavenwards for a few minutes and has imprinted upon it not only the delicate details which tease the eye of the observer and elude the skill of the artist, but also records a greater extent of celestial mist than the human eye is capable of grasping. On this account exceptional interest is attached to what has been accomplished in the portraiture of nebulæ, and the following survey of the subject will serve to show some of the roads along which progress has been made.

EARLY DAYS OF NEBULAR PHOTOGRAPHY. Dr. Henry Draper was the pioneer of nebular photography; he succeeded in obtaining a photograph of the nebula of Orion on September 30, 1880. ("Washington Observations," vol. xxv., 1878. Appendix i. p. 226.) Only the brightest parts of the nebula were comprised within the picture; nevertheless, the result was such as to show that photography had great possibilities before it as a delineator of nebula. Encouraged by the tangible fruits of his labour, Dr. Draper took a number of photographs of Orion's nebula, and in March 1881 obtained a picture showing stars fainter than the fourteenth magnitude; that is, stars only just within the limits of visibility of the telescope employed in the work. This fact was not lost upon him, for in a short note communicated to the Paris Academy of Sciences in April 1881 (Comptes rendus, vol. xcii. p. 964, 1881), he remarked that astronomers might reasonably expect to photograph stars which were quite beyond the visual reach of the most perspicuous observer; in other words, that a sensitive plate at the eye-end of a telescope could see objects which were too faint to produce any impression upon the retina of an observer using the same instrument. The picture which led to this remark was taken with an exposure of 104 minutes. Towards the beginning of the following year, a fine negative was produced by exposing a gelatino-bromide plate to the nebula for 137 minutes. This photograph comprised more of the nebulous matter, and especially of the delicate outlying parts, than any of the previous ones. In commenting at the time upon the strikingly perfect representation of the nebula afforded by the picture ("Washington Observations," vol. xxv.; Appendix i. p. 227), Prof. E. Š. Holden compared it with Bond's drawing of the same object. This observer spent several years scrutinising the nebula, and, as 'a result of his patient observation, was able to produce a picture which represented its features with greater accuracy and artistic effect than had previously been attained. Dr. Draper's photograph of the nebula was taken in a little over two hours, yet Prof. Holden confessed that for nearly every purpose it was incomparably better than Bond's hand-drawn picture. It was evident from this that a new epoch of nebular observation had been opened. Exact and automatic representations of nebula were to take the place of the strange, and often crude, drawings of these objects. The new method inaugurated by Dr. Draper has developed so much that, at the present time, it may almost be said that photography entirely holds the field as a nebula-artist.

A nebula rarely has a definite form, like the sun and moon. It presents the appearance of a cloud having more or less irregular outlines, and of which the various parts differ greatly in bright

ness.

It results from this that photographs of the same nebula may be very different in appearance, for their characters depend upon the power of the telescope employed in their production, the time during which the sensitive plate was exposed, the sensitiveness of the plate, the transparency of the atmosphere, and many other causes. While Dr. Draper was working upon the Orion nebula in America, Dr. Janssen was experimenting at Meudon with a view of determining the influence of some of the variable conditions upon the results obtained (Comptes rendus, vol. xcii. p. 261, 1881). By taking photographs with exposures of five, ten, and fifteen minutes respectively, the

eminent French investigator found that the longer the nebulous light was beating upon the sensitive film, the greater was the extent of nebulosity portrayed. It was this fact which permitted Dr. Draper to obtain his epoch-making picture, and has led to even more remarkable results during the past few years. So long ago as 1874, Dr. A. A. Common was engaged in celestial photography, but it was not until May 1882 that he exhibited a photograph of the nebula in Orion (Monthly Notices, R.A.S., vol. xliv. p. 222, 1883-84). The instrument used by him was a reflecting telescope three feet in diameter, specially constructed for photographic work. Such a large instrument is necessarily difficult to adjust and drive, and a laborious series of experiments had to be made before it could be said to be in working order. But the time spent in devising improvements was well repaid by the photograph of the Orion nebula taken by Dr. Common in January 1883. The photograph showed details of the nebula never before properly represented by the hand, and which can hardly be discerned by the eye. With the confidence that comes from experience, it was then predicted that "we are approaching a time when photography will give us the means of recording in its own inimitable way the shape of the nebula and the relative brightness of the different parts, in a better manner than the most careful hand-drawings. This prophecy was strikingly fulfilled in less than three years after it was made.

THE PLEIADES NEBULA.

In the early part of the year 1885 a fine photographic telescope was added to the equipment of the Paris Observatory, and placed under the control of two brothers, MM. Paul and Prosper Henry. The instrument had only been mounted a few months when it was used to photograph a cluster of stars-the Pleiades-which has attracted attention from time immemorial. The picture obtained showed truthfully the relative positions and grandeurs of the stars in and near the beautiful bunch of lucid points to which the telescope had been directed. But it was not so much the imprints of hundreds of stars that made the picture interesting to astronomers, as the fact that a new nebula appeared upon it. Round "stately Maia "—a star just visible to the naked eye-several wisps of nebulosity were clearly portrayed. Three further photographs of the same celestial region confirmed the existence of this nebulous matter, though no trace of haziness had previously been detected by ordinary telescopic observation (Monthly Notices, R.A.S., vol. xlvi. p. 98, 1885–86). It is a remarkable fact, however, that when an object has been discovered an observer is frequently able to see it, though he may have passed it over many times in previous surveys. So it was with the nebula round Maia. Very shortly after the announcement of the discovery had been made, M. Struve turned the 30-inch refractor at Pulkova towards the star to which attention had been directed, and found that he could distinctly see the nebulous surroundings (Comptes rendus, vol. cii. p. 281, 1886).

But faint objects are not only overlooked by the observer while viewing celestial scenery through his "optic tube"; they often go undetected on photographs themselves. The announcement of the discovery of the nebula recalled to Prof. E. C. Pickering's mind that certain irregularities had been noticed in a photograph of the Pleiades taken at Harvard College Observatory on November 3, 1885 (Astronomische Nachrichten, vol. cxiii. p. 399, 1886), that is, thirteen days before the MM. Henry obtained their first photograph showing Maia's nebulous surroundings. A re-examination of the Harvard College picture confirmed his surmise that the markings, which had previously been passed over as blemishes, were really the wisps of nebulosity photographed at Paris. Extending the scrutiny to the remainder of the Pleiades, indications of nebulous light were found about Merope, and a strange narrow streak was seen projecting from Electra. The Paris photographs showed similar appendages to these stars. This was not, however, a new discovery; the nebula near Merope was seen by W. Tempel while observing at Venice as far back as 1859 (ibid., vol. liv. p. 286, 1861), and though several astronomers unsuccessfully searched for the object, many illustrious observers had attested to its existence (Monthly Notices, R.A.S., xl. p. 622, 1879-80). Photography established the reality of Tempel's observations; and what is more, it was soon able to show that the faint patch, which had been the subject of so much discussion, was but a bright part of a vast nebulosity, in which the clustering stars were immersed. Dr. Isaac Roberts was the astronomer who brought to light