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No. 1402 (vol. xxviii.), pp. 425-460, of the Proceedings of the U.S. National Museum contains descriptions by Mr. E. A. Mearns of new mammals from the Philippine Islands. The most interesting of these is a new genus of insectivore represented by Podogymnura truei. It is allied to Gymnura and Hylomys, and has a long hind-foot and a stout tail rather more than a third the length of head and body. Two tupaias are likewise referred to a new genus, Urogale, one of these having been previously described by Mr. O. Thomas as Tupaia everetti. They are characterised by the round tail. Several new genera of rats are likewise described, for one of which the author proposes the name Bullimus, a term, in our opinion, too like the familiar Bulimus. In vol. i., No. 6, of the Bulletin of the Brooklyn Institute, Dr. J. A. Allen describes a collection of mammals from Beaver County, Utah. Copies of three other American papers have been received during the current week. In the first, Bulletin of the Brooklyn Institute, vol. i., No. 6, Mr. C. Schaeffer records additions to the beetle fauna of the United States, with notes on some previously known species. In the second, Proceedings of the U.S. National Museum, No. 1400, Miss Richardson describes two new isopod crustaceans from California. In the third, op. cit. No. 1401, Mr. T. W. Vaughan gives a critical review of the genera of the fungoid corals, with a tentative classification.
WHEN the "Book of Antelopes " was concluded in 1900 the authors were unable to give any satisfactory account of Heuglin's "giant eland" of the Bahr-el-Ghazal from the want of accessible specimens. Heuglin had described it in 1863, but had based his description on a single pair of horns, and Schweinfurth, who had subsequently met with the same animal in Bongoland, had given very little further information about it except that it had stripes on its body. In these circumstances Messrs. Sclater and Thomas classed the giant eland of Central Africa as a subspecies of the common eland (Taurotragus oryx) under the name Taurotragus oryx gigas ("Book of Antelopes," iv., p. 208). This splendid animal, which may be fairly called "the grandest of all the African antelopes," has lately been re-discovered by Mr. A. L. Butler, the superintendent of game preservation in the Anglo-Egyptian Sudan, who communicated a full description of it to the Zoological Society at a recent meeting. It appears, from the evidence given by Mr. Butler, that its nearest ally is the Derbian eland (Taurotragus derbianus) of Senegal, and not the typical T. oryx, and he therefore proposes to call it Taurotragus derbianus gigas instead of T. oryx gigas. This is probably correct, as the description given by Mr. Butler agrees very fairly in most points with the Derbian eland. But the giant eland appears to be a still larger and finer animal, with much stronger horns; its height at the withers is stated to be 68 inches. On this question we may shortly have an opportunity of forming an opinion, as Bimbashi Collins, of the Egyptian Army, who has himself shot two specimens of the animal, has sent the heads and skins to Mr. Butler to be forwarded to England, where they will probably go to the Natural History Museum at South Kensington.
THE question of the sleep of fishes was referred to (p. 104) last week in our notice of the last volume of the "Cambridge Natural History." Mr. F. Davis, writing from 49 and 51 Imperial Buildings, Ludgate Circus, E.C., says that observations of many varieties kept by him in aquaria extending over a period of twenty years show that fishes do sleep. He has also observed what appeared to
be the play or sports of fishes, which probably serves the same biological ends as in the higher vertebrates. He remarks :—“ Apparently when kept in aquaria fishes only sleep during the hours of darkness. If an artificial light be thrown upon them they quickly regain consciousness."
WE have received the annual report for 1903 of the Government bacteriologist and director of the laboratory (Mr. H. Watkins-Pitchford), Pietermaritzburg, showing that much good work is being done in the colony. It contains a valuable bacteriological report on the plague in Natal in 1902-3.
THE "Nervous Diseases Research Fund " has just issued its first annual report. The object of the fund is to promote and carry on research into the origin and cure of diseases of the nervous system. The work is carried on at the National Hospital, Queen's Square, W.C., and is under the direct supervision of the medical staff of the hospital. During 1904, forty-eight autopsies were performed and the pathological condition investigated. Special attention has been directed to the study of a disease known as myasthenia gravis, which is almost invariably fatal, and about which little is known at present.
THE development of lenticels at points where the stress is small is discussed by Mr. J. A. Terras in an article in the Transactions and Proceedings of the Botanical Society of Edinburgh (vol. xxii., part iv.), and the origin of lenticels on roots is described in some detail. A first account of new species of flowering plants from the Republic of Colombia, mostly collected by the writer, who accompanied Captain Dowding's expedition in 1898–9, is contributed by Mr. T. A. Sprague to the same number.
A RECENT leaflet issued by the Board of Agriculture and Fisheries furnishes an account of the life-history of the pine sawfly, Lophyrus pini, which attacks more especially the Scots pine and the black Austrian pine. Two broods develop in the year, the first in May and the second in August. The larvæ are the source of damage, as they devour the pine needles. Amongst the animals which feed on the larvæ are mice, squirrels, goatsuckers, and starlings, also numerous ichneumon flies. In plantations the best remedy is to kill the larvæ by hand, but as a spray for ornamental trees in parks and gardens, hellebore essence or arsenate of lead is recommended.
ALTHOUGH the investigation of the gametophytes and embryo of the gymnospermous genus Torreya has not yielded the critical results which had been expected, several interesting taxonomic characters were observed by Dr. J. M. Coulter and Mr. W. J. G. Land, and are described in their account of Torreya taxifolia in the Botanical Gazette (March). The archegonium initial is differentiated very early, while most of the endosperm develops after fertilisation. A pro-embryo of twelve to eighteen cells completely fills the egg and persists through the winter, until in the spring the suspensor elongates, and later the ruminated appearance of the endosperm becomes apparent. Rumination is shown to be due to the unequal resistance offered by the perisperm in different parts of the seed to the encroaching endosperm.
THE report of the Meteorological Commission of Cape Colony for the half-year ending June 30, 1904, has been received. The usual tables of rainfall, temperature, &c., at various stations will not be published until the issue of the next half-yearly report, so that the data may be comparable with the information contained in previous year' reports. But in lieu of the usual tables above referre
the present issue contains a very valuable series of twenty- observatory could be heard in the telephone receiver, the three tables prepared by the secretary (Mr. C. M. Stewart) | operator at the sending end merely counting one or two showing the characteristic features of the winds at the beats. On May 25 the destroyer Escopette, whilst at Brest, Cape Observatory during the five years 1896-1900, arranged was able to regulate its chronometers directly against the under sixteen points of the compass, and referred to various standard clock of the Observatory of Montsouris with an As M. Guyou points elements, e.g. temperature, humidity, &c., and giving the accuracy of about 01 to 0-2 second. percentage of relative wind-frequency and wind-force at out, owing to the wide extent of the telephone system at various hours. the present time, this mode of transmitting the time ought to be of considerable service.
WE have received a copy of the report of the director of the Philippine Weather Bureau for the year ending August 31, 1904 (reprinted from the report of the Philippine Commission, part ii.). We have frequently had occasion to refer to the useful work of this organisation, and the valuable researches and publications of the Rev. J. Algué, S.J., particularly in respect of the cyclones in the Far East. The central office performs a large amount of work gratuitously for observers on land and sea, by adjusting and comparing instruments; this is generally only known to those benefited. The director states that the weather bureau is never closed; the chief officials live at the observatory, and are ready to attend any call at all hours, especially inquiries by officers of ships, if they wish for information as to the conditions of weather. In addition to the regular work, telegrams are constantly exchanged between the provinces, China, Formosa, and Japan, and when bad weather is impending special warnings are dispatched to the points threatened.
THE annual summary of the Monthly Weather Review of the U.S. Weather Bureau for 1904, containing a useful subject, author, and title index of the papers published in the monthly parts, and an annual climatological summary of the observations made at the Weather Bureau stations, has just reached us. Weather forecasts for thirty-six and forty-eight hours in advance have been made daily throughout the year for each State, and special warnings of gales on the sea coasts have been issued when necessary. In a number of instances, the chief of the Weather Bureau states, European shipping interests were notified of the character and probable course of severe storms that were passing eastward from the American coast. The warnings and indications of the movements of West India hurricanes have evidently been the means of saving a large amount of property and a number of lives, and their value has been acknowledged by the Press, and also by the President of the Jacksonville Board of Trade, who states that the warnings to vessels not to leave port prevented serious disasters. Prof. W. L. Moore expresses the hope that the time will come when it will be possible to forecast the weather generally for coming seasons, but that time has not yet arrived. Valuable researches are being made at Mount Weather Observatory, Virginia, where it is proposed, inter alia, to discuss meteorological observations from the point of view of their relations to solar physics, and to select meteorological and magnetic elements and compare them with solar observations.
In the current number of the Comptes rendus of the Paris Academy of Sciences M. Guyou gives an interesting account of the utilisation of the telephone system for the exact transmission of time. The experiments were undertaken by the Observatory of the Bureau des Longitudes at the request of the Chambre syndicale de l'Horlogerie, and after a preliminary trial in the Paris area were extended to the whole French system. The transmission of the time by a verbal signal not being sufficiently exact for the purpose, by means of a specially arranged microphone each beat of the pendulum of the standard clock in the
IN Kungl. Svenska Vetensk. Akad. Handl. (Band 38, No. 5) Dr. Hasselberg gives the results of an investigation of the arc spectrum of tungsten. The region he has studied extends from A 3477 to A 5892. This is a continuation of the very useful series of publications by the same spectroscopist relating to the arc spectra of metals. The elimination of lines due to impurities was done by comparing the tungsten spectrum with those of other metals taken under similar conditions. In cases of close agreement between tungsten lines and those of other metals a special study was made of the lines with the object of establishing their coincidence or non-coincidence, and in the former case the probable origin of the common line was determined from a consideration of the relative intensities in the two spectra. In a comparison column are given the lines recorded by Messrs. Exner and Haschek for the same element. The strongest lines of this metal have been carefully compared with the Fraunhoferic lines, and cases of coincidence and probable identity noted.
IN our issue of July 28, 1904, we noted that Dr. H. M. Reese, of Yerkes Observatory, had published the results of some observations of "enhanced" lines in the Fe, Ti, and Ni spectra, wherein he supposed that he had discovered some enhanced lines not included in Sir Norman Lockyer's lists. In the current number of the Astrophysical Journal Mr. F. E. Baxandall comments on Dr. Reese's results, and shows that in a great number of cases there is no evidence of enhancement in the Kensington photographs. For example, the comparative tables given show for each element that of the seventy enhanced lines discovered by Dr. Reese for iron, fifteen are actually stronger in the arc than in the spark spectrum, twentyfive are equally strong in both spectra, twenty do not occur in either spectra on the Kensington grating spectrograms. whilst six are so slightly enhanced" as to leave it doubtful as to whether they should be included in this category. It seems probable that Dr. Reese was misled by comparing two spectra of which the spark was generally the stronger, for he especially remarked that only one line was stronger in his arc than in his spark spectrum.
WE have received from the Bureau of Mines of Ontario an interesting memoir on the limestones of the province by Mr. Willet G. Miller, the provincial geologist. It covers 143 pages, and contains a number of excellent photographs of the principal quarries. It shows clearly where limestones of various chemical compositions are to be found, and gives a concise account of the uses of limestone and lime at the present time. Hitherto it has hardly been realised that limestones form an important part of the mineral resources of Ontario, and this well arranged collection of analyses of limestone and of descriptions of quarries cannot fail to prove of value to all interested in the important industries that depend upon limestone as a base.
MESSRS. ILIFFE AND SONS, LTD., have published a little book on practical frame-making by Colonel W. L. Noverre; the price is IS. net.
OUR ASTRONOMICAL COLUMN. PHOTOGRAPHIC REALITY OF THE MARTIAN CANALS.-No. 4021 of the Astronomische Nachrichten contains a telegram dated May 28 from Mr. Lowell to Prof. Pickering in which the former states that several of the canals on Mars Amongst have been photographed by Mr. Lampland. others, Nilo Syrtis, Casius, Vexillum, Thoth, Cerberus, Helicon, Styx, Chaos, and Liedeus (? Libneus) are shown on the negatives, some appearing on more than twenty plates.
DISCOVERY OF SATURN'S TENTH SATELLITE.-A brief note in No. 4015 of the Astronomische Nachrichten states that Saturn's tenth satellite was discovered from an examination of several plates taken with the 24-inch Bruce telescope which were selected from those used in the determination of the orbit of Phoebe.
The new satellite appears on thirteen plates. The orbital motion is direct and the period is twenty-one days, therefore the satellite is apparently a little nearer to Saturn than is Hyperion.
JUPITER'S SIXTH AND SEVENTH SATELLITES.-An abstract from vol. xvii. of the Publications of the Astronomical Society of the Pacific, appearing in No. 4015 of the Astronomische Nachrichten, contains an account by Prof. Perrine of the observations so far made of Jupiter's sixth and seventh satellites.
The former can be photographed in ten minutes with the Crossley reflector, and thirty-six plates have been obtained. A preliminary investigation of the orbit shows that the inclination to the ecliptic and the planet's equator is about 30, and that the satellite has a period of about 250 days, with a mean distance from the planet of 7,000,000 miles. The direction of the orbital motion still remains uncertain. The brightness of the satellite indicates a diameter of about 100 miles, or less.
On examining the plates taken for the sixth satellite on January 2, 3, and 4, a much fainter object, also apparently belonging to Jupiter, was discovered, which was then situated N. and W. of, and was moving towards, the planet. Subsequent observations, which, owing to the satellite's faintness, were much more difficult to make than in the case of the sixth satellite, confirmed its dependence upon Jupiter. This object was not shown on the negatives taken for the sixth satellite during December, being just outside their field, but altogether twenty observations have been made, the last on March 9.
Apparently the orbit of the seventh satellite is quite eccentric, with a mean distance from the planet of about 6,000,000 miles and a period of about 200 days. The incination of the orbit to the plane of Jupiter's equator is about 30°, but the direction of the orbital motion is as yet undetermined. The photographic magnitude of the seventh satellite is not brighter than the sixteenth, and on comparing this with the magnitudes of other satellites and of asteroids a diameter of about 35 miles is deduced.
Prof. Perrine suggests that the large inclination of their orbits indicates that neither of these bodies were originally members of Jupiter's family, but have been captured by the planet.
STARS WITH SPECTRA OF THE ORION TYPE.-In No. 2, wl. ivi., of the Annals of the Harvard College Observatory, the distribution of stars having class B or Orion-type spectra is discussed, and all known stars of this type placed in a catalogue, in order of R.A., the position (1900), magnitude, exact type of spectrum, and the Katic longitude and latitude being given for each star. Considerably more than 30,000 spectra have been examined by Mrs. Fleming in connection with the Henry Draper "ral work, and of these 803 are included in the preset catalogue.
As a distinctive feature of these stars is the helium nated in their spectra, the allocation of them with to galactic longitude and latitude really indicates stribution of helium in the universe. On thus ing them, it is found that on dividing the sky into All areas the galactic latitudes of which are included le's en 90° and +30', +30° and o°, o° and --30°, and and -902, the numbers of well marked helium stars these divisions are 22, 219, 509, and 53, or 3. 27, 63,
and 7 per cent. of the total respectively, nine-tenths of them being within 30° of the galactic equator. A congregation in certain galactic longitudes is also indicated. Thus between 160° and 340° there are 613, or 78 per cent. of the total, of these stars. About one-quarter of the whole number are contained in four regions having a total area of 790 square degrees, or less than one-fiftieth of the sky. One of these four regions is near to the variable star I Carinæ, and lies almost wholly within the constellation Argus. As this Argus region contains nearly three times as many "Orion stars as does the Orion region, Prof. Pickering suggests that Argus stars would have been a more suitable generic name for the class of stars having spectra of thiş (B) type. He states, however, that the nebula of Orion appears to be the starting point, or origin, of class B stars, twenty of which are situated within 1° of Orionis, that is to say, nearly as many as are contained in the region between galactic latitudes +30° and +90°, although the area of the latter region is three thousand times as great.
Arranging them according to magnitude, it is found that most of this class are bright stars, only 1 in 20 being of the sixth or fainter magnitudes.
THE MOTION OF THE TAIL OF BORRELLY'S COMET (1903 iv). -From the examination of a number of photographs obtained by different observers during July, 1903, Prof. Jaegermann, Moscow, has compared the relative motions of the different sections of the tail of comet 1903 iv in regard to the movements of the comet's nucleus and to the sun. After analysing the velocities and movements determined, he has arrived at the conclusion that in this case light-pressure, acting in the sense of Arrhenius's hypothesis, was not the determining factor in the formation of the several tails, for a pressure sixty times greater than gravity would have to be assumed. If the light-pressure hypothesis be retained, the assumption must be made, according to Bredichin's idea, that the tail-matter consisted of gaseous molecules, and that its illumination was due to the fluorescence of highly illuminated gases, such as has been experimentally demonstrated by Lommel, Wiedemann, and Schmidt.
The existence of a repulsive force, other than lightpressure, was demonstrated by Bredichin in comet Rordame (1893 ii), by Prof. W. H. Pickering in comet Swift, and was confirmed by Prof. Jaegermann in a preliminary investigation concerning the denser parts of the tail of comet Swift, 1892 i.
DOUBLE STAR OBSERVATIONS.-The results of a series of observations of double stars made at Kirkwood (Indiana) Observatory are given in No. 4022 of the Astronomische Nachrichten. The observations were made by Mr. J. A. Miller and Prof. W. A. Cogshall with a 12-inch refractor, and the B.D. and A.G. numbers, the 1875 position, the magnitudes, and the measured position-angle and distance are given for each of 114 double stars.
The objects observed were selected from those noted as double by the Leipzig observers when preparing the A.G. catalogue for the zone +10° to +15°, and, with few exceptions, they have not been measured elsewhere. Some few stars suspected by the Leipzig observers as duplicate could not be seen as such by the Kirkwood observers, and one or two of the sets of measures refer to newly discovered double stars.
THE ROYAL OBSERVATORY, GREENWICH.
ON Saturday last, June 3, the Board of Visitors made their annual inspection of the Royal Observatory, Greenwich, but unfortunately, through ill-health, the Astronomer Royal was not able to be present. The following is a brief abstract of the report which was submitted to the visitors.
Very great progress has been made in the observation of the reference stars for the Greenwich section of the Astrographic Catalogue, about 9500 observations of R.A. and N.P.D. having been added during the year. The comparatively few observations required to secure five observations of each of the reference stars (more than 10,000 in number) will easily be obtained by the end of the year, as there are only 5 stars requiring three observ
ations, 100 requiring two, and 1500 requiring one observation only in order to carry out the programme. In fact, it may be taken that the observations for this catalogue are practically completed. The catalogue, which will be terminated this year, will contain, besides the reference stars for the Astrographic Catalogue, the 834 zodiacal stars given in the Nautical Almanac for 1897.
It is proposed to begin next year a new nine-year catalogue of the stars of magnitude 9.0 and brighter between the limits +24° to +32° of N. declination, this being the Oxford astrographic zone, for which they serve as reference stars. The re-observation of these stars, which for the most part fall within the Cambridge zone of the Astronomische Gesellschaft Catalogue, will afford valuable data for their proper motions, besides giving fundamental positions for the Oxford astrographic plates.
The comparison between theory and the Greenwich meridian observations of the moon from 1750 to the present time, undertaken by Mr. Cowell, has been completed for the longitudes, and the discussion from 1847 to 1901 is completed for the latitudes. The only point left outstanding is the motion of the node, for which it is necessary to discuss as long a series of observations as possible. The results obtained for the longitudes are summarised in a series of papers in the Monthly Notices of the Royal Astronomical Society. In particular, the paper in vol. lxv., No. 2 (1904 December), gives the coefficients of 145 terms as obtained directly from observation, with a comparison with the theoretical coefficients given by Hansen, Delaunay, M. Radau, and Dr. Hill. The publication of the details of the whole investigation will be shortly proceeded with.
The re-reduction of Groombridge's observations completed at the date of the last report, and during this year the printing of the results has been pushed on. The introduction has also been prepared for press. A discussion of the proper motions determined by comparison with modern Greenwich observations, and a determination of the constant of precession and of the direction of the solar motion by Mr. Dyson and Mr. Thackeray, are given in the Monthly Notices of the Royal Astronomical Society, March.
The altazimuth has been in regular use throughout the year, and a second determination of the pivot errors has been made, and also observations for obtaining the value of one revolution and errors of the screw of the telescopemicrometer have been completed.
The observations of the moon, both in and out of the meridian, seem very satisfactory as shown by the agreement between the two instruments, the transit circle and the altazimuth.
The 28-inch refractor has been employed, as was the case last year, for micrometric measurements of double stars, the total number measured being 603. Of these, 143 have their components less than 10 apart, and 60 less than o".5. A marked deterioration of the images of the stars led to an examination of the lenses, and the suspected tilt. between the components was corroborated and remedied.
Sixty-five photographs of Neptune and its satellite have been secured with the 26-inch refractor, while, with the 30-inch reflector, numerous photographs of minor planets and comets a, b, c 1904, and a 1905, have been obtained.
At the date of the last report, 119 plates taken of Eros with the astrographic equatorial, and 55 taken with the Thompson equatorial, had been measured. During this year the remainder of the photographs have been measured, making in all 198 with the astrographic equatorial and 152 with the Thompson instrument. The reduction of the measures is in a satisfactory state, and it is expected that it will be completed in two months for both sets of photographs.
The astrographic equatorial has been employed mainly to obtain photographs to replace chart plates which show slight photographic defects unsuitable for production of enlarged prints.
The measurement of the catalogue plates for the Greenwich section is now completed. Since the last report 47,200 measures of pairs of images (6m. and 3m.) have been made. The number of plates measured in the year is 102, covering 128 square degrees between declination
83° and the pole. The number of plates measured up to the date of last year's report was 1051. Adding the 102 plates measured this year, the total number of plates measured is 1153, being the 1149 of the Greenwich section +4 additional photographs of the polar field.
For the year ending 1904 December 31, Greenwich photographs of the sun have been selected for measurement on 209 days, and photographs from India and Mauritius (to fill up the gaps in the series) on 151 days, making a total of 360 days out of 366 on which photographs are at present available. Photographs were taken in Mauritius for three of the six days yet unrepresented, and may be received in due course.
The solar activity has shown a great increase during the year ending 1905 May 10, and the sun has not been free from spots on a single day during that period. The mean daily spotted area for 1904 was more than half as great again as that for 1903, and early in the present year number of exceptionally large groups was observed. The group which was seen first on the east limb on 1905 January 28 had a greater total area than any other group which has been photographed at the Royal Observatory. The principal results of the magnetic elements for 1904 are as follows:
In 1904 there were no days of great magnetic disturbance and eight of lesser disturbance.
The mean temperature for the year 1904 was 49°8, or 0°3 above the average for the fifty years 1841-90. During the twelve months ending 1905 April 30 the highest temperature in the shade (recorded on the open stand in the magnetic pavilion enclosure) was 91°.0, on August 4On the same day the highest temperature in the Stevenson screen in the magnetic pavilion enclosure was 89°5, and in the observatory grounds 89°.7. The lowest temperature of the air recorded in the year was 19°5, on January 1. During the winter there were thirty-nine days on which the temperature fell below 32°-0, being seventeen less than the average number.
The mean daily horizontal movement of the air in the year ending 1905 April 30 was 280 miles, which is 2 miles below the average of the preceding thirty-seven years. The greatest recorded daily movement was 867 miles, on November 9, and the least 49 miles, on December 22. The greatest recorded pressure of the wind was 23.5 lb. on the square foot, on March 12, and the greatest hourly velocity 45 miles, on December 30.
The number of hours of bright sunshine recorded during the twelve months ending 1905 April 30, by the CampbellStokes instrument, was 1486 out of 447 hours during which the sun was above the horizon, so that the mean proportion of sunshine for the year was 0-333, constant sunshine being represented by 1.
The rainfall for the year ending 1905 April 30 was 20-21 inches, being 4.33 inches less than the average of the fifty years 1841-90. The number of rainy days was 153. This small rainfall may be contrasted with the heavy rainfall of 35-42 inches in the corresponding period last year. The most striking contrast is obtained by comparing the rainfall for the year commencing 1903 March 1, which was more than 37 inches, with that for the year commencing 1904 March 1, which was less than 171 inches. This dry period of twelve months was followed by a heavy rainfall in 1905 March, which exceeded 3} inches, and is the greatest amount recorded in March since 1851.
The printing of the Paris-Greenwich longitude determination, 1902, is practically complete. The Killorglin longitude is the only determination which still requires to be printed to complete the volume of longitude determinations, which will contain the determinations Paris-Greenwich made in 1888, 1892, and 1902, of GreenwichWaterville-Canso-Montreal made in 1892, and of Greenwich-Killorglin made in 1898.
The re-reduced Groombridge Catalogue is nearly completely printed, with the exception of the introduction, which is ready for the press.
Provision has been made in the Navy Estimates for the observation of the total solar eclipse of 1905 August 30 by a party of three observers on the coast of Tunis, where the weather conditions are promising. It is proposed to take photographs of the corona for detail and extension with the Thompson 9-inch coronagraph, the 13-inch astrographic refractor, and the 4-inch Dallmeyer rapid rectilinear lens, and also photographs of the spectrum with the two spectroscopes lent by Major Hills, R.E., as in 1900 and 1901.
THE OPTICAL CONVENTION.
THE optical convention has just concluded
The first group of papers dealt with the design of
Dr. Drysdale gave a general account of the aberrations of lens systems, submitting a classification and specification of the various aberrations to obtain an expression of opinion from those working at Chalmers gave a graphical method of representing the the subject. Mr. results of calculations of lens systems, and a modification of the Hartmann system of testing to permit of measuring and expressing aberrations in exactly the same This should make it possible to obtain the relation between the definition and the measured or calculated aberrations. In the discussion Mr. Carson pointed out the importance of the relative intensity of the image disc and the aberration patch in estimating the performance of lenses.
Mr. Walter Rosenhain criticised the mechanical design of certain types of instruments; he showed that, in many cases, the ideals of the instrument maker were in conflict with sound engineering principles, and suggested directions in which improvements might be looked for.
Diffraction in optical instruments was discussed by Mr. JW. Gordon in an important theoretical paper; his conclusions, which would modify many of our ideas on optical systems, are now being submitted to a definite experimental
A group of papers related to interference phenomena. Mr. J Rheinberg exhibited a method of producing achromatic interference bands which is likely to have numerous applications. Mr. Stansfield described a simple form of Machelson interferometer specially suitable for demonstraton. Prof. Watkin and Mr. Morrow exhibited apparatus for calibrating extensometers by observing the d'splacement of interference bands.
Mr Twyman described the manufacture of the Echelon spectroscope, stating the accuracy required in the plates and the precautions used to obtain it. This apparatus was exhibited and compared with the Lummer plate" arrangement for obtaining resolution of spectrum "parallel Mr. Blakesley discussed the various forms of prism which could be used in constant deviation spectroscopes and some of their applications. Mr. Newall dealt with astronomical spectroscopes, demonstrating that the limits usefulness of the present type of spectroscope were supost reached in the case of faint stars, as the intensity fight necessary for photographing their spectra can only be obtained at the sacrifice of the purity of the spectrum ur the certainty of identification of the lines, and that no ry marked improvement is likely to be obtained from The use of larger objectives, on account of the increased absorption in the prisms required. He suggested the use
Lord Rayleigh dealt with the subject of polish, pointing the distinction between the process of grinding, which consists of the removal of comparatively large flakes, and
that of polishing, which he regards as molecular, the rough
esses of the surface being reduced to dimensions smaller than the wave-length of light. Experiments on the thickNO. 1858, VOL. 72]
ness of glass removed by polishing and by etching with hydrofluoric acid under various conditions were illustrated. In the discussion Mr. Walter Rosenhain cited evidence to show that the surface flow which has been recognised in the polishing of metals also occurs in glass.
Mr. Walter Rosenhain dealt with the possibilities of
A number of instruments for optical measurements were
Mr. Baugh described the use of invar tapes for base-
Dr. Drysdale discussed the requirements of small tele-
Mr. A. C. Jolley gave a critical review of photometric
Mr. Milne exhibited his new form of spectrophotometer. The apparatus is especially suitable for determinations of the absorption of light of specified wave-length by liquids.
Mr. Bull discussed the theory of tricolour filters, plates, and inks. He concluded that it was most satisfactory to adjust each independently of errors in the adjustment of the others. The filters should have a certain amount of overlap, the colour of the overlap of two filters being the colour of the printing ink corresponding to the other filter.
Mr. Crawley discussed the limits of stereoscopic vision;
Mr. H. L. Taylor discussed the effects of astigmatism
Dr. Walmsley gave an account of the attempts which
Major-General Waterhouse gave an account of the history
In the evening lecture, Prof. Silvanus P. Thompson gave