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MR. Rosewater, who was a distinguished member of the the other hand, it is smaller in front, especially to the south-east U.S. Military Telegraph Corpi during the American civil of a minimum, and further from the centre. (5) Compared to war, and is now President of the Old Timers Telegraphic Asso- the general circulation of the air in a barometric minimum, the ciation, has lately been studying the various Government radiation of the upper clouds most resembles the direction of the telegraph systems in use in Europe. The re-ults of his investi. wind near the earth's surface. The meaning of this last sentence gations will shortly be submitted to what is expected to be an is not obvious ; but the other conclusions agree, on the whole, unusually interesting and important meeting of the New York with the views of other meteorologists who have studied the Electric Club.

subject. A COPY of “Whitaker's Almanack for 1892" has been sent THE Meteorologische Zeitschrift for November contains a to us a few days in advance of publication. Great care has been summary, by Dr. J. Hann, of the meteorological observations taken, as usual, to keep the Almanack up to date. Additional taken at Cairo from 1868-88. The observations have been space is devoted to educational matters, and for the first time published in extenso, together with a good introduction upon educational progress and occurrences are dealt with in a separate the climate, in the Bulletin of the Egyptian Institute, and although article. There is also a separate article on agricultural educa- similar observations have occasionally been published before, tion. Other subjects separately treated are the rise, progress, the present series contains much new and useful material. The and achievements of the great lines of ocean steamers, naval most striking feature in the climate of this part of Egypt is the gunnery, and the results of the census. Of course, various Chamsin, the hot and dust-bearing wind which makes its sections resemble in subject those of former years, but even appearance in March or April for about ihree to four days at a these are for the most part entirely fresh in substance. In many time, and robs a large portion of the trees of their leaves. In instances the changes wrought during the interval of a single the intervals during which this wind is not blowing the year are so numerous that scarcely a line of the section in which weather is pleasant and clear during spring-time, and the the subject is treated remains unaltered.

nights fresh and calm. During the summer the north winds Owing to his declining to take up his residence in Rio de prevail, with high temperature, very clear air, and great dryness. Janeiro, Dr. Fritz Müller, of Blumenau, Sta. Catharina, has

Towards September humidity appears with the rise of the Nile, been summarily dismissed by the new Government of Brazil

the ground is at times covered with heavy dew, and the heat from his post of "Naturalista viajante" to the Museum at Rio

becomes oppressive on account of the moi-ture. In October de Janeiro. The great services which Dr. Müller has rendered and November fog occasionally occurs in the morning, and rain both to zoological and botanical science during his forty years' begins to fall. After this season the temperature is uniform residence in Brazil are too well known and too widely acknow and pleasant. Snow is unknown, frost very seldom occurs, and ledged to need dilating on. Dr. F. Müller is now close on

rain is nut very frequent.

The absolute maximum temperature completing his seventieth year; and Dr. Karl Müller, of Halle, of the 21 years period was 117° in August 1881, which was the editor of Natur, proposes to seize the opportunity of col

also closely approached in May 1880, viz. 116°:4. The absolecting from his fellow-naturalists some substantial recognition lute minimum was 28°:4 in February 1880, and the mean of the honour in which he is held.

annual temperature was 70°.5. Rainfall is only given for the

years 1887-88, in which o 87 and 167 inches fell respectively. DR. H. E. Hamberg has communicated to the Swedish The relative midity sinks at times even on a daily average to Academy of Sciences a paper on the radiation of the upper 12 per cent., and has been known to fall as low as 3 per ceni. clouds round barometric minima, prepared from the cloud at certain hours. Thunderstorms and hail are very rare. The observations available at Upsala Observatory for the years original work contains a long investigation on the connection 1874-89. The arrangement of the highest clouds-cirrus and bei ween the height of the Nile and the weather, a comparison cirro-stratus—in the form of parallel bands has long been between the present climate and that at the beginning of this noticed by meteorologists in this country, and various papers on century, and several carefully prepared diagrams referring to all the subject have been written by Mr. W. C. Ley, MM. Hilde meteorological elements. brandsson, Köppen, and others; and the movements of these clouds, in conjunction with the wind prevailing at the earth's The refraction and velocity of sound in porous bodies allowing surface, are at times sufficient to determine approximately the passage of sound, such as sponge, wadding, felt, &c., have been direction in which an atmospheric disturbance exists, even with recently made a subject of investigation by Herr Hesehus (Rep. out the use of synoptic charts. For instance, a barometric der Physik). His plan was to make a plane convex spherical minimum often exists in a direction nearly perpendicular to that lens of iron wire net, and fit it, filled with the porous body of the radiation, and, generally, on that part of the horizon where (variously condensed), into an aperture in a screen. A pipe of the bands of upper clouds are most dense, or whence they seem variable tone was sounded on one side, and the behaviour of a to radiate, but it always necessary to take into aecount the sensitive flame noted on the other. From the distance of the direction of the wind at the earth's surface. The author draws focus, when found, could be deduced the refractive index and the the following conclusions from his investigation :-(1) The radia- velocity in the lens. The refrangibility grows with increasing tion of the upper clouds is closely connected with barometric density of the porous substance, while the velocity on the average minima. (2) Near a barometric minimum, with the pressure is lessened ; the latter is also less, the greater the sound-wave. The below 29.9 inches, the radiation forms with the radius of the author gives details of experiments in which the velocity varied depression an angle of about 70°, the deviation of the radiation from 146 to 261 metres per second (with ebonite shavings). from the direction of the surface wind being positive (i.e. 10 the From an empiric formula which he gives, he makes deductions right), by some degrees, on the south-west of the barometric regarding the propagation of sound in tubes, considered as only minimum, and negative on the south-east of it. (3) Further

a special case of its spread through the pores and passages of a from the barometric minimum, with a pressure of 29.9 inches and porous body.

He hopes further research in this field may above, the inclination to the radius is rather greater, about 75°, do something to elucidate the passage of light and electricity except where the barometric minimum lies to the north of the through media. place of observation, in which case it is much lower. (4) The The Report of the United States Commissioner of Education angle formed by the radiation is generally greater in the rear of a has been submitted to the Secretary of the Interior. It says barometric minimum, reaching nearly 90° in a high pressure; on that the usefulness of the Bureau depends directly upon what it prints and publishes, and therefore urges an appropriation of been shaded with mats or canvas alter becoming ripe. The best 30,000 dollars for general printing for the fiscal year 1892-93, way to lengthen out the season of gooseberries, Mr. Thomson and makes a special request for a specific appropriation of says, is to plant a portion of a wall with a due north aspect 20,000 dollars to continue the series of educational histories of with some Warringtons, and train them on the multiple-cordon the several States. The Commissioner reports that there were system, and keep the laterals spurred in precisely the same way enrolled in 1889-90 in the public schools of the United States as is adopted with red currants on fences or walls, or in fact of elementary and secondary grade 12,686,973 pupils, as against with gooseberry bushes grown in the ordinary way. The main 9,867,505 in 1880. The enrolment formed 20:27 per cent. of shoots should not be closer than 10 inches. If a coping of the population of 1890. The average daily attendance of pupils wood be placed on the wall to throw off wet, a net being used on each school day in 1890 was 8,144,938. The whole number to protect the fruit fronı birds, the gooseberries can be kept fresh of public school teachers in the past year was—males, 125,602 ; till far into October, and are then very useful and acceptable. females, 233,333. The total amount expended during the past The authorities responsible for the working of the free public fiscal year for public school purposes was 140,277,484 dollars, libraries of Manchester cannot complain that these institutions is against 63, 396,666 dollars in 1870, and 78,004,687 dollars in are inadequately appreciated. From the Thirty.ninth Annual 1880. The expenditure per capita of population in 1880 was Report on the subject to the Council of the city we learn that, 1.56 dollars, while in 1890 it was 2.24 dollars.

during the year ended September 5, 1891, the number of visits THE U.S. Bureau of Education has issued, as one of its made by readers and borrowers to the Manchester libraries and “Circulars of Information,” an excellent paper on " Sanitary reading rooms reached an aggregate of 4,327,038, against a Conditions for Schoul-houses,” by Albert P. Marble, Superin total for the preceding twelve months of 4, 195, 109. The numtendent of the Public Schools of Worcester, Mass. Dr. Marble ber of volumes lent for home reading was 702,863. Of these, has for many years studied the problems of ventilation, heating,

only thirteen are missing. lighting, draining, and school-house construction ; and his sug

At a recent meeting of the Chemical Section of the Franklin gestions are well worthy of consideration in this country, as well Institute, Dr. Bruno Terne read a paper on the utilization of as in America. The value of the Circular is increased by an the by-products of the coke industry. In the course of his reappendix, in which are given a number of designs of school marks he said it seemed strange, and nevertheless was a fact, buildings of various sizes, carefully selected with a view to com- that, with all the ingenuity of the American people in the admodiousness, healthfulness, and economy of construction. In vancement of the purely mechanical part of the technical an official statement prefixed to the Circular, attention is espe industries, they have been and are still slow in the development cially called to a series of nineteen plates constituting the prize of chemical industries. “If,” said Dr. Terne, “ you will visit designs selected and published by the State of New York in our coal region to-day, you will find the nightly sky illumined 1888.

from the fires of the coke ovens, and every one of the brilliant

fires bears testimony that we are wasting the richness of our In the interesting paper on insectivorous plants, read before land in order to pay the wiser European coke manufacturer, the Royal Horticultural Society on September 22, 1891, and who saves his ammonia and sends it to us in the form of sulphate now published in the Society's Journal, Mr. R. Lindsay refers of ammonia ; and who also saves his tar, which, after passing to the experiments by which Mr. Francis Darwin has shown the through the complex processes of modern organic chemistry, amount of benefit accruing to insectivorous plants from nitro- reaches our shores in the form of aniline dies, saccharin, nitrogenous food. Mr. Lindsay says his own experience in the benzol, &c.” Dr. Terne thinks that every pound of ammonia culture of Dionæa is that when two sets of plants are grown side used in America ought to be produced there, and that every by side under the same conditions in every respect, except that pound of soda should be made from American salt wells by the insects are excluded from the one and admitted to the other, the ammonia process. latter, or fed plants, are found to be stronger and far superior to

MR. COLEMAX SELLERS contributes to the December num. the former during the following season. He points out the im- ber of the Engineering Magazine, New York, the first of a portance of remembering that the natural conditions under series of articles on what he calls “American Supremacy in which these plants are found are different from what they are Mechanics.” Incidentally, he notes that most English invenunder cultivation. In their native habitats they grow in very tions brought to the United States have to be “ Americanized, poor soil and make feeble roots, and under these conditions may simplified, made accessible in the case of machinery, and conrequire to capture more insects by their leaves to make up for structed with a view to ease of repair as well as to durability their root deficiency. Under culture, however, fairly good roots when ander the care of careless attendants.” Mr. Sellers does for the size of plant are developed. “Darwin,” says Mr. not think it would be worth the while of Americans to copy Lindsay, “ mentions that the roots of Dionæa are very small; the solidity and immense weight that some deem a merit in those of a moderately fine plant which he examined consisted

English machinery." of two branches, about one inch in length, springing from a bulbous enlargement. I have frequently found Dionæa roots

ACCORDING 10 the “World's Fair Notes,” sent to us from six inches in length ; but they are deciduous, and I can only has been making excavations in the mounds of Ohio, made an

Chicago, the party which, under the direction of Mr. Putnan, conjecture that the roots mentioned by Darwin were not fully grown at the time they were measured. What is here stated of important discovery on November 14. While at work on a the natural habits of Dionæa applies more or less to all insecti- mound 500 feet long, 200 feet wide, and 28 feet high, the vorous plants."

excavators found near the centre of the mound, at a depth of

14 feet, the massive skeleton of a man incased in copper armour. GOOSEBERRIES are so much liked by most people that it is very The head was covered by an oval-shaped copper cap; the jaws desirable the season for them should, if possible, be prolonged. had copper mouldings; the arms were dressed in copper, while According to Mr. D. Thomson, who has a good paper on copper plates covered the chest and stomach, and on each side gooseberries in the current number of the Journal of the Royal of the head, on protruding sticks, were wooden antlers ornaHorticultural Society, this can be done easily in the northernmented with copper. The mouth was stuffed with genuine part of Great Britain. At Scotch shows it is quite usual to see pearls of immense size, but much decayed. Around the neck fine fresh gooseberries about the middle of September. These, was a necklace of bears' teeth, set with pearls. At the side of as a rule, are gathered from ordinary bushes that have perhaps this skeleton was a female skeleton.

a

ACCORDING 10 a telegram received in New York from Mexico, MM. H. LÉVEILLÉ AND A. SADA, of Pondicherry, have started the Mexican Government has ordered the inhabitants of the a new bolanical journal with the title Le Monde des Plantes : villages in the neighbourhood of the town of Colima to abandon Revue Mensuelle de Botanique. The first number appeared on their homes and seek refuge elsewhere, as the volcano in the October 1. It is published at Le Mans (Sarthe). vicinity, which was recently in eruption, shows signs of fresh activity, and the country sor miles around it is illuminated by volume of “Studies in Anatomy.” It is edited by Prof. A. H.

The Council of the Owens College have published the first the flames issuing from the crater.

Young, and presents a part of the results of investigations con

ducted in the anatomical department of the College during the Tue census of 1890 in Austria-Hungary shows that the rate

last three or four years. at which the population increased during the preceding ten years was very different in the two great divisions of the Messrs. BAILLIÈRE, TINDALL, AND Cox have issued Monarchy. The increase in so-called Cisleithania was 79 second edition of Dr. Edridge-Green's work on “Memory : Its per cent. ; in Transleithania, 10·82 per cent. In the indi. Logical Relations and Cultivation." vidual provinces the increase was very unequal. In Lower Austria it was 13-8 per cent., this high rate being due to the

A new edition of "Falling in Love : with other Essays on attractive force of Vienna. Then came Bukowina with 13:1

More Exact Branches of Science," by Mr. Grant Allen, has

been published by Messrs. Smith, Elder, and Co. per cent. ; Galicia, 104 per cent. ; Silesia, 6'5 per cent. ; Moravia, 5'5 per cent. ; Bohemia, 5 per cent. ; the Alpine Messrs. BEMROSE AND Sons have issued a second edition of lands, from 3-2 to 3-6 per cent. ; and Tyrol, o'9 per cent. A a “ Hand-book to the Geology of Derbyshire," by the Rev. different set of figures is yielded by the increase of the various J. Magens Mello. The work has been rewritten, and is illusnationalities. Among these the Poles stand highest, with 15 trated with a map and sections. per cent. ; then the Serbo-Croatians, 14 per cent; the Ru.

A CURIOUS compound of lead, sodium, and ammonia, thenians, 11 per cent. ; the Germans, 5-66 per cent. ; the Pb. Na. 2NH3, is described by M. Joannis in the current number Czechs, 5'65 per cent. ; the Slovenians, 3-18 per cent. ; and

of the Comptes rendus. M. Joannis has been studying the nature the Italians, under i per cent.

and reactions of the substance known as sodammonium, obMR. HENRY LAVER records in the current number of the

tained by dissolving metallic sodium in liquefied ammonia. The Zoologist the capture of a spotted eagle at Elmstead, near

deep blue liquid thus produced has been shown in a previous Colchester, on October 29, 1891. On that day a farm labourer

communication (see NATURE, vol. xliii. p. 399) to decompose saw a strange bird, evidently in an exhausted condition, alight slowly at the ordinary temperature into hydrogen gas and in the field in which he was working. When he went after it, sodamide, a compound of the composition NaNH,, which M. it rose, and flew about a hundred yards. He soon came up to Joannis isolated in the form of colourless crystals. That such a it, and, after some little difficulty, from its pugnacity, captured compound as sodammonium (NaNH3),, really exists in the blue it alive and uninjured, and in a few days sold it to a gipsy, who

solution in liquefied ammonia would appear to be the most in turn disposed of it to Mr. Pettitt, the local taxidermist. Mr.

natural assumption from these experiments. The reactions of Laver says its plumage appears to indicate good health, and that

sodammonium now described lend additional support to this its appetite favours that idea. If any injury led to its caplure,

view. When a rod of pure lead is placed in a saturated solution all marks of it have quite disappeared.

of sodammonium in water, the reddish-brown liquid becomes

rapidly blue, and finally assumes a deep green tint. A small The new instalment of the Transactions of the Leicester quantity of hydrogen is evolved at the same time owing to the Literary and Philosophical Society (vol. ii. part ix.) contains decomposition of a portion of the sodammonium into sodamide, an abstract of an interesting lecture by Mr. Harold Littledale, as above described. The lead gradually disappears, and a solid of the College, Baroda, on some of his experiences with big substance possessing an indigo-blue colour is deposited. This game in India. Mr. Littledale gave an especially good account

blue substance is found upon analysis to consist of the compound of shooting in the Himalayas. The ibex and markhoor were

Pb Na. 2NH3, and would appear to be a sodammonium in found at altitudes varying from 10,000 to 20,000 feet, and could

which a portion of the sodium is replaced by lead. It dissolves be obtained only by perseverance in the face of many dangers readily in liquefied ammonia with formation of a solution and obstacles. Of the markhoor (Capra megaceros), a splendid possessing a bottle-green tint. It is not very stable, dissociating animal which is becoming increasingly rare, he obtained ten

spontaneousiy on standing, with production of a grey substance examples, and ibex had also fallen to his gun, with 45

very much resembling spongy platinum. Upon exposure to air inch horns—the maximum development being about 52 it becomes warm owing to its rapid oxidation. It behaves in a inches. Various species of sheep also occurred, as the magni. somewhat remarkable manner towards water. When intro ficent Ovis poli, which the lecturer had not yet met with, Ovis duced in small quantities at a time into ordinary water, the first ammon, Ovis cyclocerus, &c. The chamois was found com- portions dissolve completely, the oxygen dissolved in the water monly in the Himalayas, and Hodgson's antelope could be | oxidizing the lead to litharge, which at once dissolves in the shot at elevations of 20,000 feet. Amongst the other mountain alkaline solution formed. As soon, however, as the oxygen in animals described were the snow leopard, Sikkim stay, and the water is used up, further additions of the substance result in musk deer (Moschus moschiferus), with its tusks about 5 inches the precipitation of black Rocculæ of metallic lead. Another in length.

interesting reaction of sodammonium is that with metallic

mercury, which behaves in an entirely different manner from MR. W. H. ROSSER has written for the benefit of candidates lead. When the solution of sodammonium in liquefied ammonia preparing for the Board of Trade examinations a general ex. is poured over a globule of mercury, rapid action occurs, with planation of what is usually known as the “Compass Syllabus." the ultimate elimination of the whole of the ammonia, and It is entitled “Compass Deviation : a Syllabus of Examioation production of a sodium amalgam of the composition NaHgs, in the Laws of Deviation, and in the Means of Compensating which has been obtained in well-formed crystals. This reaction it,” and is published by Messrs. James Imray and Son. The is the more interesting inasmuch as M. Berthelot, from purely pamphlet is to be regarded as an appendix to Mr. Rosser's thermo-chemical considerations, has previously indicated the “Deviation of the Compass considered practically."

possible exi tence of such a compound of sodium and mercury.

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The additions to the Zoological Society's Gardens during the Astronomische Vachrichten, No. 3068, contains the following past week include a Sooty Mangabey (Cercocebus fuliginosus $) ephemeris for the comet Tempels-Swift for 12h. Paris mean from West Africa, presented by Mr. H. E. Dampier, J.P. ; a Rufous-necked Weaver-Bird Hyplantornis textor 8 ) from

Log a. West Africa, presented by Commander W. M. Latham, R.N., |

I 38 47

+27 4 45 94220 F.Z.S. ; a White Stork (Ciconia alba), European, presented by

IS
46

13 33 Mr. Walter Chamberlain, F.Z.S. ; eighteen Grenadier Weaver

19
53 10

94339 Birds (Enslectes oryx), ten Golden-backed Weaver Birds

013

27 3 (Pyromelana aurea), nine Black-capped Weaver Birds

31 55 9-4467

35 32 (Hyphantornis nigriceps), four Red-bellied Waxbills (Estrelda

23

38 4

94606 rufiventris), three Triangular-spotted Pigeons (Columba guinea),

24
27 19

39 24 four Dwarf Chameleons (Chameleon pumilus) from South

25
33 47

39 50 984753 Africa, presented by Mr. R. W. Murray.

26

40 7
27
46 19

37 59 9 4907 28

35 47
OUR ASTRONOMICAL COLUMN.

29
58 17

32 57

9'3068

30 JUPITER AND HIS FIRST SATELLITE.-A series of observa.

3 4 5

29 24 31

9 43 tions of spots and markings on the planet Jupiter were communi

25 2. 9-5235 cated to the Royal Astronomical Society at the November

Astronomische Nachrichten, No. 3069, contains a paper by meeting by Mr. Barnard. A careful study of numerous details Prof. Pickering on the distribution of energy in stellar spectaa. observed during a period of twelve years has led to the con. Since stellar magnitudes obtained by various processes, such as clusion that the red colour of any of the markings is an photography, eye-observations, &c., cannot be co wpared when indication of their age ; or in other words, when a spot or

The light of stars is of different colours, the method he promarking (other than the white spots first appears it is dark or poses is to adopt a single wave-length in the spectrum to which black, but after some time turns red.” Several examples are

all intensities should be referred, a curve or series of numbers given of this transition, and the great red spot seems to be no exception to the rule. Measurements of transits of the broken wave-length. For rays of different wave-lengths he says:

being necessary to give a measure of the rays of each different chain of small black spots just north of the north equatorial belt, * The intensities may be determined by comparing the densities discovered by Mr. Barnard during the present year, show that of different portions of the photographic spectrum.”. The line the spots have a very large relative motion, for they complete a revolution around Jupiter in about thirty-seven days. The centre of the photographic spectrum.” The photographs he

fixed upon was that of the hydrogen line G, "as it is near the oblong du ky spot discovered near the great red spot last year employed were those forming part of the "Henry Draper is diminishing its longitude by about o°54 per day, and so com Memorial, all taken under similar conditions, and in each one pletes a revolutioa relatively to the latter in about 167 days. separately twenty points were taken and compared by comThis, and other new red markings in the southern hemisphere, parison with a standard photographic wedge. Each of the seem to have their origin in the region of the great red spot. Their period of rotation is about the same as the round white and the measure, corresponding with that of the hydrogen

measures thus obtained was converted into logarithmic intervals, spots in the same hemisphere, the longitudes of which diminish line G of wave-length 434, was deducted. By subtracting by about o° 6 per day. The observations show that the great the values of the logarithm of the energy of the solar light, the red spot is stationary in longitude, and possibly shorter and remainder showed the excess or deficit of energy of the star broader now than in 1880. "Further observations of the first as compared with that of the sun, eliminating the various sources satellite have been made in order to throw light upon the of error enumerated above." In the table below we give the apparent duplicity of this body in transit, distinctly seen by Mr.

results for three stars as obtained by Prof. Pickering :Bamard on September 8, 1890. It is noted :-" The phenomena seen on these occasions would rather discourage the idea A. Log E.

a Can. Maj.

E. of actual duplicity. At these times the satellite has appeared 390

- 0'26

+ 0'37 + 0*32 - 0:57 0:55 egg-shaped when in relief on the dark belt. . . . I am con- 400

0:19

+ o'c8 - 0:38 ... 0°65 fident that this particular phase, and perhaps also that of

410

+ 0'03 023 0-76 apparent duplicity, is explained by a bright belt on the satellite 420

- 0'07

0.85 or by darkness of the polar regions, which is the same thing.”

430

0'95 Mr. Stanley Williams has suggested that the phenomenon 440

+ 0'05 I'os observed on September 8, 1890, may have been due to the satellite having been seen in transit as a dark spot close to a dark spot on the surface of Jupiter which transited at the same time.

SPECTRA OF THE SUN AND METALS.-Some extremely The values in the second column representing the logarithm fine comparative photographic spark-spectra of the sun and

of the energy of the solar light, while those in the last one metallic elements were exhibited by Mr. F. McClean at the

represent the energy of sunlight itself. Thus in the case of meeting referred to in the above note. The specira extend, in

a Orionis, the energy for the wave-length 390 is represented six sections, from 1 3800 to 1 5750—that is, from about L of the by - 0:57, sunlight being 0-55. The absolute energy is found solar spectrum lo near D. They are divided into two series, by adding the tabular number to that given for sunlight in one containing spectra of the sun, iron, platinum, iridium, the second column," so that we have - 0.26 - 0'57 = - 0:83, osmium, palladium, rhodium, ruthenium, gold, and silver ; the corresponding to a ratio of oʻ15. Thus the energy of the light other containing spectra of the sun, iron, manganese, cobalt, of a Orionis of wave-length 390 is only about one-seventh of nickel, chromium, aluminium, and copper. The scale of wave- that of wave-length 434. length adopted is that of Ångström's map. Since the spark was In this number, also, Mr. Truman Saffard contributes a paper taken in air all the spectra have air-lines running through them. on the observation of North Polar stars in the vertical of Polaris. The purest materials obtainable were used as electrodes : After mentioning the difficulty of observing polars in the daynevertheless a large number of lines due to foreign substances time, of connecting other polars with double transits of Polaris, appear on the photographs. The commonesto impurity is and of the independence ihat now exists in the various Polar calcium, its lines being present in very nearly all the spectra. catalogues, he describes a method which tends to eliminate No attempt has been made to eliminate the lines having their many of these deficiencies. It consists in adjusting a transit so origin in such impurities ; hence, as Mr. McClean remarks, it is that Polaris will be near its centre wire at eastern elongation, impossible "to obtain any complete results from these two which takes place about 19h. 23m. sidereal time, and the two series of photographs alone. Photographs of the spectra of all stars Camelopardalis 25 H and Schwerd 1172 (Carrington 2965), the common oxidizable metals, and particularly of calcium, which pass the same vertical within about half an hour of this barium, magnesium, and titanium are first required."

time, the latter above Pole, earlier than the Pole-star reaches

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be elongation, the former, below Pole, later. In this way the for producing such fringes, by providing the cap of the ght ascension of Polaris plays a small part in its azimuth of with two parallel slits, adjustable in width and distalongation, which is dependent solely on the declination and If such a combination be focussed on a star, then, insie titude. Assuming the present declinations of the two stars concentric rings before mentioned, there will be

entioned, with probable errors of < =0":2 and = 0"-3 re. straight equidistant bands whose length is paralle. pectively, he finds that the right ascension would probably be slits, the central one being brightest,' Fig. 1, c.

error by + 0.002s. and = 0'0043. In fact, the probable The general theory of these fringes may be sum Erors “dependent upon anything but the transit of the star to Philosophical Magazine for March 1891. The gene e determined will be much less if the present method is used showing the relation between the visibility of the fri with an equal instrument), than if stars in the same declination, distance between the slits is: at opposite Polaris in right ascension, were observed by direct mparisons in the meridian." By applying this method to

Q(x) cos kx dx

X ther stars of different right ascensions and gradually increas.

V?= ng declinations," as the R.A. of Polaris or its opposite is pproached, numerous co-ordinates thoroughly independent can e obtained, and will “provide zero points for the proposed umber of photographic plates 2° square, and consequently help

which reduces to the simpler form settle the places of all stars in that region.”

(x) cos kx dx

VE
TEASUREMENT OF JUPITER'S SATELLITES
BY INTERFERENCE.

when the object viewed T has long been known that even in a telescope which is

symmetrical.

A number of applications of this formula are theoretically persect, the image of a luminous point is comosed of a series of concentric circles with a bright patch of confined to the case in which the object viewe

former paper, but for the present purpose at ght at the common centre. This system of circles can easily | projection) is a circular disk, uniformly illunina e observed by examining any bright star with a telescope pro

In this case equation (2) becomes ded with a circular diaphragm which diminishes the effective perture. The appearance of the image is shown in Fig. 1, a. the case of an object of finite angular magnitude the image

V= Vi-w2.coS vuld be constructed by drawing a system of such rings about

dw

ao Dery point in the geometrical image. The result for a small isk (corresponding to the appearance of one of the satellites of in which a is the angular diameter of the obje upiter as seen with a 12-inch telescope whose effective aperture smallest angle resolvable by an equivalent aper

ratio of a light-wave to the distance between u Fig 1

The curve expressing this relation is given in the ordinates are values of the visibility of th abscissæ are the corresponding values of the

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a

as been reduced to six inches) is given in Fig. 1, b; the chief oints of difference between this and Fig. 1, a, being the greater ize of the bright central disk, and the lesser clearness of the sur. bunding rings. The larger the disk the more nearly will the apmearance of the image correspond to that of the object ; and the maller the object the more nearly does it correspond with Fig. 1, a, and ihe more difficult will be the measurement of its ctual size. Thus, in the case just cited, the actual angular iameter is about one second of arc, and the uncertainty may

From this it will appear that the fringes d mount to half this value or even more. The relative uncertainty, other things being equal, will be less disappearances were noted, and the average

intervals, and in a laboratory experiment a proportion to the increas: in the aperture, so that with the 6-inch telescope the measurement of the diameters of Jupiter's value of a, the angular magnitude of the

less than two per cent. atellites should be accurale lo within ten per cent. under favour

From the curve it is evident that the ble conditions. It is important to note that in all such measurements the image

most readily and accurately observed, and bserved is a diffraction phenomenon--the rings being intererence fringes, and the ettings being made on the position of

-= 1'22;

ao hat part of a fringe which is most easily identified. But such

whence, putting s for the distance betw measurements must vary with the atmospheric conditions and especially with the observer-for no two observers will agree

slits, and taking for the wave-length of tł pon the exact part of the fringe to be measured, and the un

spectrum o‘0005 mm., and dividing by

in radians we have ertainties are exaggerated when the fringes are disturbed by tmospheric tremors.

138 If, now, it be possible to find a relation between the size of he object and the clearness of the interference fringes, an indemendent method of measuring such minute objects will be fur- In consequence of the kind invitat. wished ; and it is the purpose of this paper to show that such a Holden, it was decided to make a pract. nethod is not only feasible, but in all probability gives results of the proposed method at Mount Ham. ar more accurate than micrometric measurements of the image.

These will be superposed on another set of In a paper on the "Application of Interference Methods to

the edges of the slits; but the latter are too ! Astronónical Measurements”, an arrangement was described confusion.

2 l he wave-length will, <f course, vary some ' Philosophical Magazine, July 1890.

but may be made constant by interposing a red

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