MR. W. W. SMITH, writing to the new number of the Entomologist from Ashburton, New Zealand, says that he has for twelve years successfully used hellebore as an insecticide. It is used annually by many orchardists in the South Island for destroying the larvæ of Tenthredo (Selandria) cerasi. Mr. Smith uses it in the proportion of half an ounce to a bucket of water. When he notices the newly-hatched larvæ on the leaves, he carefully and effectually syringes the trees with the solution, choosing a calm day for doing so. The larvae are equally common on the cherry-, plum-, and pear-trees, and rapidly destroy the foliage if they are not checked or destroyed. One good syringing suffices. When the trees are syringed early, the imago sawfly is prevented from laying eggs further on the foliage, and by this course much labour is avoided. He does not go over the trees syringing a second time with pure water, as the particles of powder left adhering to the foliage are invariably washed off by rains before any of the fruit ripens.

MR. J. W. FEWKES contributes to the January number of the American Naturalist, just received, an interesting paper on the ceremonial circuit of the cardinal points among the Tusayan Indians. During the progress of the secret ceremonials which are performed in the Kib-vas or Estufas at Hual-pi, and other pueblos of the old province of Tusayan, it is customary for a priest to pass on the north side of the fire-place as he approaches the altar, and on the south as he passes from the altar to the ladder. This custom is conscientiously followed by the older priests, especially when taking part in important ceremonials; and Mr. Fewkes has seen novices, and even old priests, corrected and sent back when they had violated this simple Kib-va custom. The four directions do not correspond with the true cardinal points. The so-called Kwi-ni-wi-ke of the Hopi is neither the magnetic nor the polar north, but about north-west, or 45° west of north, and the other points vary in the same ratio. Mr. Fewkes thinks that a ready explanation of this is found in the orientation of the Kib-vas, which, in turn, depends on the extension of the mesa upon which Hual-pi is situated-or, speaking more accurately, as he says in a note, on the direction of the lines of fissure of the rock of which the mesa is built up. The ceremonial circuit is constantly followed in the preparation of so called medicine. When a priest pours the liquid of which it is made into the terraced rectangular bowl, preparatory to placing the other ingredients in it, he pours the fluid first on the north side, then on the west, then on the south, then on the east side of the bowl. The ceremonial circuit is followed in connection with many other observances noted by Mr. Fewkes. He also remarks that the following colours correspond to the four cardinal points (bearing in mind that the Hopi north is really north-west): north, yellow; west, blue (represented ceremonially by malachite green); south, red; east, white. The priest of the antelope assemblage, in making the sand mosaic picture a few days before the snake dance, first makes the yellow border, then the green, then the red, then the white. The north line of the yellow is followed by the west of the same colour, then the south, then the east. The same sequence occurs when he outlines and makes the body of the semicircular clouds in the centre of the mosaic (dry painting). The lightning serpents of the four colours are made in the same order of the colours. It is interesting to note, as Mr. Fewkes says, that the ceremonial circuit is opposite that of the sun in its daily course in the sky. He thinks it is probably more than a coincidence that it is the same circuit which the snake and antelope priests take when they move about the place, and the latter carry the snakes in their mouths.

LAST year Dr. J. T. Rothrock received from the American Philosophical Society a grant of 300 dollars to defray part of the expenses of a trip to the West Indies. The object was the

collecting of photographs and information which could be utilized in the preparation and delivery of the annual lectures popularly known as "the Michaux forestry course. About 150 good negatives were obtained, and there are about 75 satisfactory illustrations of the trees, physical geography, and topography of the islands visited. The trip lasted three months. Dr. Rothrock was particularly struck by the contrast between the Bahamas and Jamaica. In the course of some interesting observations printed in the latest instalment of the Proceedings of the American Philosophical Society, he points out that the Bahamas are low and show no considerable elevation, while Jamaica reaches a maximum altitude of 7360 feet above the sea-level. The soil of the Bahamas is scanty, and consequently cultivation entails fertilization. That of Jamaica is of great depth, and its continued productiveness is evidence of a vast natural fertility. The flora of the Bahamas shows marked resemblance to that of Florida. The flora of Jamaica is essentially tropical, save at such altitudes as suit plants of cooler regions. In such places are found the common chickweed (Stellaria media), the white clover (Trifolium repens), associated with plants from the cooler parts of southern regions. The mangrove (Rhizophora mangle), common to the tropical seas around the globe, attains in Jamaica (compared with that in Florida and in the Bahamas) a surprising height. Near Port Morant are large jungles, where the trees attain a height of at least 60 feet. Dr. Rothrock calls attention to possible tannin production from the mangrove. No tree in North America, he says, at all approaches the mangrove in the percentage of tannin it contains. That the mangrove should have remained so long unutilized is due to the difficulty of obtaining its tannin free from colouring matter. Dr. Rothrock thinks that in the near future, owing to exhaustion of other tannin-producing trees, the arts will be forced to draw upon the mangrove, even if an improved chemistry is not able to free it from this objectionable colour. The natives obtain a red-brown dye from the bark by simply steeping it in water.

Mr. T. SouthwELL, Norwich, records in the April number of the Zoologist that he was lately informed, by Mr. D. C. Burlingham, of the occurrence of a male Greenland shark, (Lamargus borealis), which measured 14 feet 2 inches in length and weighed 1 tons, at Lynn, on the 21st of January last. It was found stranded on a sand-bank on the east side of the Bulldog Channel, and was brought up to Lynn by a fishing-smack, being still alive when Mr. Burlingham saw it. It was subsequently exhibited at Cambridge, and its owner intended to take it to Huntingdon, Peterborough, and elsewhere. This species is of rare occurrence on the Norfolk and Suffolk coast, and the present example is only the fourth of which Mr. Southwell has

notes.

DR. E. RÁTHAY states that the galls of Cynips calycis, produced on Quercus pedunculata, attract, by their viscid secretion, a number of small ants, which he believes to be advantageous to the tree, in killing quantities of caterpillars and other insects which are its natural enemies. He illustrates the value of this protection by the statement that the inhabitants of a single ants' nest may destroy in a single day upwards of 100,000 insects.

IN the Bullettino of the Italian Botanical Society, Signor F. Pasquale proposes a new theory of the morphology of the carpel in flowering plants, founded on an extended observation of the course of the vascular bundles. According to him, a carpel is not a single modified leaf, but is the result of the concrescence of three, less often of two, leaves, which take part in the formation and in the nutrition of the ovules and of the seeds. The carpel is therefore a triphyllome, of which one leaf (the inferior one) is sterile, and the other two (superior) are fertile; and between these there is an intimate fusion, with complete anastomosis of the vascular bundles. Each fertile

leaf is composed of a membranous portion, the placental hemiphyll, and an ovular hemiphyll, which is entirely transformed into the ovules with their funicles, together with the style and stigma. The placental hemiphyll also takes part in the formation of the pericarp and septa. The ovules originate from the whole of the ovular hemiphyll, and not merely from the carpellary margins or teeth.

We notice the appearance of a very useful work, in Russian, by Prof. Samokvasoff, on Russian prehistoric antiquities, under the title of "Foundations of a Chronological Classification of Antiquities, and Catalogue.' As seen from the title, the work consists of two parts: a catalogue of the very rich collection of the Russian Professor, partly illustrated, and a general description of the various epochs which may be distinguished in the relics of the past on the territory of Russia. He has no difficulty in showing that the Slavonians of the first centuries of our era were by no means mere savages. The burial places of that period, usually situated close to the earthen forts, some of which must have required the work of a considerable population, contain hundreds and thousands of graves, so that it is certain that the Slavonians of that period were living in large societies, and had their fortified towns. The same burial customs prevailed over large areas, but the treasures now unearthed from various graves show that differences of wealth and social position existed at that time as well. Considerable amounts of Greek, Roman, and Arabian gold and silver coins were found in the graves, the metal alone of the coins found in some graves attaining, at its present prices, the value of several hundred pounds; while numbers of objects of art, of Greek, Roman, Byzantine, and Arabian origin, are proofs of the brisk foreign trade which took place at that time. The graves of the pagan Slavonians contain flax, woollen, silk, and gold-embroidered tissues; ornaments in gold, silver, bronze, and bone; iron weapons and parts of armament; gold, silver, bronze, iron, and clay vessels, and so on; while the sickles and the grains of wheat, oat, and barley which were found in the graves of South Russia, together with small idols and other objects devoted to pagan worship, are proofs of agriculture having been carried on during the pagan epoch.

Two new liquids containing fluorine have been synthesized by M. Meslans. They are halogen derivatives of glycerin, and were obtained by allowing allyl fluoride, a gaseous substance recently described by M. Meslans, to react with chlorine and bromine. Allyl fluoride, C3H5F, is readily prepared by the gradual addition of allyl iodide to dry silver fluoride. It is a colourless gas of peculiar odour, which burns with a luminous flame upon ignition, with liberation of vapour of hydrofluoric acid. When a jet from which chlorine is escaping is brought into a vessel filled with allyl fluoride, combination at once ensues, and drops of a colourless liquid commence to be deposited upon the walls of the vessel. In order to obtain the liquid in greater quantity a large flask is employed, through the caoutchouc stopper of which pass two tubes, one delivering chlorine and the other allyl fluoride. Considerable heat is developed during the act of combination, hence the flask is immersed in a bath of cold water. A slight excess of chlorine is maintained during the reaction, and the liquid which rapidly collects is consequently coloured green; but when sufficient has been accumulated the supply of chlorine is first arrested in order that the excess of that gas, which produces the green coloration, shall be converted to the colourless liquid by the still-issuing allyl fluoride and the liquid thus decolorized. The colourless mobile liquid so obtained is then submitted to distillation, when practically the whole passes over into the receiver between 122° and 123 ́. If the synthetical preparation is conducted volumetrically, it is found that equal volumes of allyl fluoride and chlorine unite;

THE second new compound is analogous to the one just described, and resembles it very closely in properties. It is obtained by the direct union of bromine with allyl fluoride. If a few drops of bromine are allowed to fall into a vessel filled with allyl fluoride, the latter is rapidly: absorbed with considerable rise of temperature, the red colour of the bromine simultaneously disappearing. To prepare the liquid in quantity, allyl fluoride is allowed to stream slowly into a quantity of bromine contained in a cooled flask, the operation being continued until the red colour of the liquid has entirely disappeared. The colourless liquid thus obtained distils without decomposition at 162°-163°. The data afforded by determinations of the bromine content and the vapour density point to the formula C3H5FBг. Both the liquids above described appear to be very stable compounds, for even during their distillation the glass vessels containing them exhibit no signs of etching. They are miscible with ether, and readily soluble in absolute alcohol, but they are almost perfectly insoluble in water. They possess pleasant odours, somewhat reminding one of chloroform, and are sweet but burning in taste. They are incombustible, but at a high tem perature the vapours burn with liberation of hydrofluoric and hydrochloric or hydrobromic acids.

THE additions to the Zoological Society's Gardens during the past week include a Guinea Baboon (Cynocephalus sphinx ?), a Bateleur Eagle (Helotarsus ecaudatus), a Puff Adder (Vipera arietans) from South Africa, presented by Mr. Keith Anstruther; a Japanese Deer (Cervus sika ?) from Japan, presented by Sir Douglas Brook, Bart.; a Wedge-tailed Eagle (Aquila audax) from Australia, presented by Miss Carr; a Tawny Owl (Syrnium aluco), European, presented by Mr. E. A. Rocheda; a Puff Adder (Vipera arietans) from South Africa, presented by Mr. D. Wilson; two Common Vipers (Vipera berus), British, presented by Mr. W. H. B. Pain; a Shielded Eryx (Eryx thebaicus) from North Africa, deposited; four Topela Finches (Munia topela) from China, a Black-necked Swan (Cygnus nigricollis) from Antarctic America, purchased.

OUR ASTRONOMICAL COLUMN.

THE RELATIVE MOTION OF 61 CYGNI.-The large proper motion of 61 Cygni, combined with its remarkable duplex character, renders it an object of great interest. Doubts have been expressed, however, as to whether the two components are really connected by a bond of mutual attraction, and it has been assumed that they will gradually separate and traverse widely different paths in space. Prof. A. Hall has brought together and distance of the star since 1825, and has investigated them all the observations which have been made of the position-angle with a view of setting this question (Astronomical Journal, No. 258). The result is in favour of the physical connection of the two stars, but all that can be said of the period of revolution is that it is very long. The mass of the brighter star appears to be 3'4 times that of the companion.

THE TEMPERATURE OF THE SUN.-Numerous attempts have been made to determine the sun's temperature, and the results obtained range from 1500 to 5,000,000. The enormous differences that exist between the different estimates result from the fact that different laws have been assumed to represent the rate of radiation. M. H. Le Chatelier communicated the latest contribution to the subject at the meeting of the Paris Academy of March 28. His experiments show that the intensity

of the radiations emitted by an incandescent body of which the emissive power is unity is expressed by the formula

I =

106'7 T 3210 T'

The temperatures employed range from 680° to 1770°, and these, with the observed intensity of radiation, have been used to plot a curve. By extending the curve and measuring the intensity of the radiation from the sun, an estimation of 7600° as the effective solar temperature is obtained. The term effective temperature is used to express that temperature which a body having an emissive power equal to unity should possess, in order to send out radiations of the same intensity as the sun. The real temperature of the photosphere is higher than 7600°, because its radiations are absorbed by the cooler solar atmosphere, and it may be, also, because the emissive power of the sun is less than unity.

COMET SWIFT, MARCH 6.-The following ephemeris for this comet is given in Astronomische Nachrichten, No. 3082, for 12h. Berlin mean time :

14 ,, 15

5 57 50*48

60 52'27 6223°43 6 3 54'78

- 0 7 21.8 -0 2 7'1 +o 3 0.9 +0 8 2'1

+O 17 44'3 +0 22 25'I PERIODIC PERTURBATIONS OF THE FOUR INNER PLANETS. -In the astronomical papers which are prepared for the use of the American Ephemeris and Nautical Almanac (vol. iii., part v.), most valuable computations of the periodic perturbations of the longitudes and radii vectores of the four inner planets of the first order as to masses are contributed. Prof. Newcomb, under whose directions these computations were made, tells us in the introductory note that in the preparation of the fundamental data for the new tables, all the coefficients, which are included in the expressions for the general perturbations, were redetermined the values obtained for them agreed well with those obtained by Leverrier, and prove that their accuracy is placed beyond doubt. To eliminate any errors that might have been made, duplicate computations were undertaken, and the results of them both are given in the final expressions for the perturbations in longitude. It may be stated that the complete theory is not here published, the secular variations, perturbations of the latitude, and those of long period in the longitude, not being printed, owing

to their unfinished state.

:

N.P.D.'S OBSERVED WITH GREENWICH AND WASHINGTON TRANSIT CIRCLES.-Prof. Newcomb, under whose direction these computations were made, gives in vol. ii. part vi. of the same series of papers just referred to an interesting discussion on the differences that have been found in these observations. Those made with the Greenwich circle cover a period of thirty-six years, from 1851-87, while the Washington observations are included in the years 1866-86. The author has a firm basis here, on which he can rely, for in the former series the same methods of reduction and observation were in use for this entire period without interruption. He inquires first of all into the conclusions which can be gathered from the stability of the instrument, from both direct and reflection observations, and finds that the R-D corrections are mainly due to flexure. The constant of refraction and the possible periodic error due to those in the graduation of the circle are then dealt with, together with corrections for reductions to the equinox during the years 1851-56. The hypothesis of the

secular change in the latitude is here considered as too improbable for acceptance with our present data, so that the apparent variations are here supposed to be due to the changes in the instrument or habits of the observers. In the section on the latitude of the Royal Observatory, he finds that the co-latitude derivable from observations of the four polar stars during the period 1877-86 is greater by o" 31 than that derivable froin observations of all circumpolar stars. At the conclusion of this investigation he gives a table showing the corrections to the north polar distances, derived annually from the observations with the Greenwich transit circle, to reduce them to the instrumental standard of the present paper, and the Pulkowa refractions. WASHINGTON OBSERVATIONS, 1887.-All the observations which were made during the year 1887 at the United States Naval Observatory are included in this volume. The introduction, besides giving the report of the Superintendent on the state of the Observatory generally, contains all the detailed information relative to the methods of computing the observations made with the transit circle, meridian transit instrument, and the 26-inch and 9.6-inch equatorials. The principal work of the transit circle during this period has been upon the sun, moon, and planets, and miscellaneous stars. These last, included stars of the American Ephemeris for clock corrections, &c.; stars whose occultations were observed at this Observatory, and by the various American parties that observed the 1874 transit of Venus; those selected for standard stars in the formation of the catalogue made from 1846-49; and stars of the B.A.C. between 120° o' and 131° 10' N.P.D. that have not been observed three times in R. A. and declination at Washington. The meridian transit instrument was devoted to the determination of the errors of the standard mean time clock in connection with the transmission of time, and 1645 transits were taken. The clock's rate was found satisfactory, its variations following closely those of the barometer. The 26-inch and 9'6-inch equatorials have been also used, the former for observations of double stars and small stars in the Pleiades, the latter for comets. Besides these, many other magnetic and meteorological observations are recorded, but a brief account of them will be found in the

notes.

FERTILIZATION OF THE CASUARINACEÆ.

FEW recent articles in botanical literature can compare in interest and importance with that contributed by Dr. Melchior Treub to the tenth volume of the Annales du Jardin Botanique de Buitenzorg, "On the Casuarinacea, and their Position in the Natural System." The startling announcement is made of the occurrence of a mode of fertilization of the ovule essentially different from that which takes place in other flowering plants.

order, are about twenty-three in number, and are trees, nearly The species of the genus Casuarina, which alone make up the all natives of Australia, where they are known as "beef-wood trees," characterized by their jointed, almost leafless branches. From the catkin-like inflorescence of very imperfect flowers, they are generally placed among Incomplete or Monochlamydea, near to Myricaceae and Juglandaceæ. The female flower is composed of two carpels, without either calyx or corolla, and has at the base an ovarian cavity, in which are formed (in C. suberosa) the two ovules with parietal placentation, but connected from the first with its summit by cords of cellulose. Corresponding to the style in most plants, is an axial mass of tissue which M. Treub calls the stylar cylinder, surrounded by a peripheral region containing tracheides, and terminating in two elongated stigmas. The two ovules are unequal in size, and coalesce in their growth by their placental portions; the connection between them and the base of the stylar column is called the bridge; they are also connected with the base of the ovarian cavity by their funicles.

The processes which take place within the ovule up to the time of the formation of the embryo-sac are very different from those hitherto observed in Angiosperms. Several large hypodermal cells, the archespore-cells, at the summit of the nucellus, divide tangentially; and two of the cells thus produced towards the inner side, the primordial mother-cells, divide further, giving rise to a thick cylinder of large cells occupying the centre of the nucellus, the sporogenous tissue, surrounded by flattened cells corresponding to the "Tapetenzellen" of Goebel. The cells of the sporogenous tissue are equivalent to the mother-cells of the embryo-sac in other Angiosperms. These cells divide transversely into large megaspores (macrospores); the small inactive

cells become absorbed. In C. glauca and Rumphiana tracheides are formed, analogous to the elaters of the Hepatica; their function is uncertain. The megaspores, or embryo-sacs, of which there are usually from sixteen to twenty, lengthen in the direction of the chalaza, some of them sometimes penetrating and forming "tails" between the elements of the fibrovascular bundle of the funicle. The sister-cells of the embryo-sacs, instead of being absorbed at an early period, as in other Angiosperms, disappear only much later. The megaspores which develop fully divide at the end into two or three cells, which are in most cases naked, and result from the division of a single cell. In the great majority of cases only a single megaspore in each nucellus has these terminal or sexual cells furnished with cell-walls; this is the future embryo-sac. The oosphere is always formed from the sexual cell which has the thickest wall. No antipodals are formed.

Only a single ovule is ever fertilized, and the pollen-grain which fecundates it advances towards the embryo-sac in a way entirely different from anything that occurs in other Phanerogams. The pollen-tube does not enter the ovarian cavity; it descends the stylary cylinder, crosses the bridge and the tissue which unites the ovule with the wall of the ovary, and arrives at the fibrovascular bundle which leads to the chalaza, where it produces two short branches, then traverses the chalaza, and enters the ovule by means of the "tail" of a sterile megaspore, and continues its course towards the embryo-sac. Towards the middle of the nucellus it contracts, tapers off, and ruptures, the terminal fecundating portion becoming separated from the rest of the pollen-tube.This portion, which has a thickened wall, and contains distinct protoplasm, never enters the micropyle or the embryo-sac, but becomes firmly attached to the wall of the latter, at a spot variable in position, but always at some distance from the sexual apparatus. Dr. Treub has not, at present, been able to detect in this portion a definite nucleus, or to follow the actual process of fecundation. During the development of the embryo-sac, numerous endosperm-nuclei are formed, and subsequently the embryo makes its appearance. The mode of development of the embryo does not differ from that which occurs in other Dicotyledons.

The peculiar processes which accompany the act of fecundation, and the presence of a large number of megaspores, each containing a sexual apparatus, induce Dr. Treub to regard the Casuarinaceæ as a distinct group of Angiosperms, of equal rank with the Monocotyledones and Dicotyledones together, and he proposes the following primary classification of Phanerogams :I. GYMNOSPERMS.

OXFORD.-Endowment of Original Research.-The following notice has been received by the Vice-Chancellor :-A gentleman has established a Scholarship of £100, tenable for one year, for the encouragement of original research. The Scholar will be selected by a Committee composed of Dr. George Thin, Surgeon-General Cornish, and Prof. A. Winter- Blyth. The conditions of the Scholarship are, that the research be on a subject requiring for its elucidation both chemical and bacteriological methods, and the subject will be selected by the Committee of Selection. With the concurrence of the Scholar, the work is to be done in the laboratories of the College of State Medicine, 101 Great Russell Street, W. C., and the Scholar will have to devote his whole time to the work. Application to be made to Surgeon-General Cornish, on or before April 18, 1892. In a Convocation held on April 5, it was decreed (the Council of the Royal Geographical Society having offered a further sum of £150 a year, to be met by an equal sum from the University, for the payment of a Reader in Geography

during the next five years) that the offer be accepted, and that the thanks of the University should be conveyed to the Counci of the Royal Geographical Society for their liberal offer.

The programme of the fifth summer meeting of University Extension and other students, to be held in Oxford in July and August 1892, has been issued, and in its general character resembles that of last year. The inaugural lecture will be delivered by Mr. John Addington Symonds (if his health permits) on Friday, July 29, at 8.30 p.m. The meeting will, as in former years, be divided into two parts, viz. from July 29 to August 9, and from August 10 to August 26. In Natural Science the following arrangements have been made :

In Chemistry: a course of eighteen days' practical instruction in the University laboratory, limited to 100 students, conducted by Messrs. J. E. Marsh and A. D. Hall of Balliol College.

In Geology: a special course of fourteen days' practical instruction, with field work provided, if at least 40 students offer themselves.

:

In Botany in addition to lectures on primroses and their relations, it is proposed to arrange, for a class of not less than 40 students, a three weeks' course of practical instruction.

In Biology: to the same minimum number of students is offered a special course of lectures and demonstrations in the physiological laboratory, to form an introduction to the study of life, and especially of nervous organisms.

Courses of lectures and instruction on Astronomy, Mechanics, Sound, Light and Heat, Electricity, Physiography, and Hygiene can be arranged.

It is also announced that there will be no summer meeting in 1893, as during August in that year the Examination Schools will be in the hands of workpeople.

ST. ANDREWs.-Summer Session.-A course of lectures in zoology and botany, qualifying for graduation, will commence on May 2, the former by Prof. Prince, the latter by Mr. Robertson, the University Lecturer on Botany. These are open to students of either sex.

SOCIETIES AND ACADEMIES. LONDON.

Royal Society, March 31.-"Aberration Problems: a Discussion concerning the Connection between Ether and Matter, and the Motion of the Ether near the Earth.' By Oliver Lodge, F. R.S., Professor of Physics, University College, Liverpool.

The paper begins by recognizing the distinction between ether in free space and ether as modified by transparent matter, and points out that the modified ether, or at least the modification, necessarily travels with the matter. The well-known hypothesis of Fresnel is discussed and re-stated in modern form.

Of its two parts, one has been verified by the experiment of Fizeau, the other has not yet been verified. Its two parts are, (1) that inside transparent matter the velocity of light is affected by the motion of that matter, and (2) that immediately outside moving matter there is no such effect. The author proceeds to examine into the truth of this second part, (1) by discussing what is already known, (2) by fresh experiment.

The phenomena resulting from motion are four, viz.:—

(1) Changes in direction, observed by telescope and called aberration.

(2) Change in frequency, observed by spectroscope and called Doppler effect.

(3) Change in time of journey, observed by lag of phase or shift of interference bands.

(4) Change in intensity, observed by energy received by thermopile.

After a discussion of the effects of motion in general, which differ according as projectiles or waves are contemplated, the case of a fixed source in a moving medium is considered; then of a moving source in a fixed medium; then the case of medium alone moving past source and receiver; and, finally, of the receiver only moving.

It is found that the medium alone moving causes no change in direction, no change in frequency, no detectable lag of phase, and probably no change of intensity; and hence arises the difficulty of ascertaining whether the general body of the ether is moving relatively to the earth or not.

A clear distinction has to be drawn, however, between the effect of general motion of the medium as a whole, and motion

of parts of the medium, as when dense matter is artificially moved. The latter kind of motion may produce many effects which the former cannot.

A summary of this part of the discussion is as follows:Source alone moving produces a real and apparent change of colour; a real but not apparent error in direction; no lag of phase, except that appropriate to altered wave-length; a change of intensity corresponding to different wave-lengths.

Medium alone moving, or source and receiver moving together, gives no change of colour; no change of direction; a real lag of phase, but undetectable without control over the medium; a change of intensity corresponding to different distances but compensated by change of radiating power.

Receiver alone moving gives an apparent change of colour; an apparent change of direction; no change of phase, except that appropriate to extra virtual speed of light; change of intensity corresponding to different virtual velocity of light.

The probable absence of a first order effect of any kind, due to ethereal drift or relative motion between earth and ether, makes it necessary to attend to second order effects.

The principle of least time is applied, after the manner of Lorentz, to define a ray rigorously, and to display the effect of existence or non-existence of a velocity potential. Fresnel's law is seen to be equivalent to extending the velocity potential throughout all transparent matter.

It is shown that a ray traversing space or transparent substances will retain its shape, whatever the motion of the medium, so long as that motion is irrotational, and that in that case the apparent direction of objects depends simply on motion of observer; but, on the other hand, that if the earth drags with it some of the ether in its neighbourhood, stellar rays will be curved, and astronomical aberration will be a function of latitude and time of day.

The experiment of Boscovich, Airy, and Hoek, as to the effect of filling a telescope-tube with water, does not discriminate between these theories. For if the ether is entirely non-viscous and has a velocity potential, stellar rays continue straight, in spite of change of medium (or at oblique incidence are refracted in the simple manner), and there will be no fresh effect due to change of medium; while, if, on the contrary, the ether is all carried along near the earth, then it is stationary in a telescope tube, whether that be filled with water or air, and likewise no effect is to be expected. In the case of a viscous ether, all the difficulty of aberration must be attacked in the upper layers above the earth; all the bending is over by the time the surface is reached. It is difficult to see how an ethereal drift will not tend to cause an aberration in the wrong direction.

Of the experiments hitherto made by Arago, Babinet, Maxwell, Mascart, Hoek, and perhaps others, though all necessary to be tried, not one really discriminates between the rival hypotheses. All are consistent either with absolute quiescence of ether near moving bodies, or with relative quiescence near the earth's surface. They may be said, perhaps, to be inconsistent with any intermediate position.

Two others, however, do appear to discriminate, viz. an old and difficult polarization experiment of Fizeau (Ann. de Chim. et de Phys., 1859), which has not been repeated since, and the recent famous experiment of Michelson (Phil. Mag., 1887) with rays made to interfere after traversing and retraversing paths at right angles.

The conclusions deducible from these two experiments are antagonistic. Fizeau's appears to uphold absolute rest of ether; Michelson's upholds relative rest, i.e. drag by the earth.

The author now attempts a direct experiment as to the effect of moving matter on the velocity of light in its neighbourhood; assuming that a positive or negative result with regard to the effect of motion on the velocity of light will be accepted as equivalent to a positive or negative result with respect to the motion of the ether.

He gives a detailed account of the experiment, the result of which is to show that such a mass as a pair of circular saws clamped together does not whirl the ether between the plates to any appreciable amount, not so much, for instance, as a 1/500th part of their speed. He concludes, therefore, that the ether is not appreciably viscous. But, nevertheless, it may perhaps be argued that enormous masses may act upon it gravitationally, straining it so as perhaps to produce the same sort of effect as if they dragged it with them. He proposes to try the effect of a larger mass. Also to see if, when subject to a strong magnetic field, ether can be dragged by matter.

The aberrational effect of slabs of moving transparent matter is considered, also the effect of a differently refractive medium. Motion of medium, though incompetent to produce any aberrational or Doppler effect, is shown to be able to slightly modify them if otherwise produced.

The Doppler effect is then entered into. The question is discussed as to what the deviation produced by a prism or a grating really depends on: whether on frequency or wave-length. It is shown that whereas the effect of a grating must be independent of its motion and depend on wave-length alone, yet that the effect observed with a moving grating by a moving observer depends on frequency, because the motion of the observer superposes an aberrational effect on the true effect of the grating. This suggests a means of discriminating motion of source from motion of observer; in other words, of detecting absolute motion through ether; but the smallness of the difference is not hopeful.

Michelson's experiment is then discussed in detail, as a case of normal reflection from a moving mirror or from a mirror in a drifting medium. No error in its theory is discovered.

The subjects of change of phase, of energy, of reflection in a moving medium, work done on a moving mirror, and the laws of reflection and refraction as modified by motion, are considered.

It is found that the law of reflection is not really obeyed in a relatively moving medium, though to an observer stationary with respect to the mirror it appears to be obeyed, so far as the first order of aberration magnitude is concerned; but that there is a residual discrepancy involving even powers of aberration magnitude, of an amount possibly capable of being detected by very delicate observation.

The following statements are made and justified :

(1) The planes of incidence and reflection are always the

same.

(2) The angles of incidence and reflection, measured between ray and normal to surface, usually differ.

(3) If the mirror is stationary and medium moving, they differ by a quantity depending on the square of aberration magnitude, i.e. by 1 part in 100,000,000; and a stationary telescope, if delicate enough, might show the effect.

(4) If the medium is moving and mirror stationary, the angles differ by a quantity depending on the first power of aberration magnitude (I part in 10,000), but a telescope moving with the mirror will not be able to observe it; for the commonplace aberration caused by motion of receiver will obliterate the odd powers and leave only the even ones; the same as in case (3).

(5) As regards the angles which the incident and reflected waves make with the surface, they differ in case (3) by a first order magnitude, in case (4) by a second order magnitude.

(6) At grazing incidence the ordinary laws are accurately obeyed. At normal incidence the error is a maximum.

(7) The ordinary laws are obeyed when the direction of drift is either tangential or normal to the mirror, and is disobeyed most when the drift is at 45°.

(8) In general, the shape of the incident wave is not precisely preserved after reflection in a moving medium. To a parallel beam the mirror acts as if slightly tilted; to a conical beam as if slightly curved. But either effect, as observable in the result, is almost hopelessly small.

(9) Similar statements are true for refraction, assuming Fresnel's law.

The possibility of obtaining first order effects from general ethereal motion by means of electrical observations is considered.

Chemical Society, March 17.—Dr. W. J. Russell, F. R.S. Vice-President, in the chair.-The following papers were read :-A study of the conditions which determine combination between the cyanides of zinc and mercury, and of the composition and properties of the resulting double salt, by W. R. Dunstan. When a solution of zinc sulphate is added to one of mercuric potassium cyanide, HgK2(CN), or when mercuric chloride is added to a solution of zinc potassium cyanide, ZnK (CN), a white precipitate is formed, which has been stated, on the authority of Gmelin, to consist of a double cyanide of zinc and mercury of the formula ZnHg(CN),. This, however, is not the case. The maximum amount of mercuric cyanide that can be retained by the precipitate is only 38.5 per cent., and is dependent on the amount of water present during precipitation as well as on the proportions in which the salts interact. When