SPECTROSCOPIC NOTES.

Arrangements for observing the total eclipse of May 28 have been so far completed as to insure adequate observation by well equipped expeditions. Most of the large observatories will be represented by observing parties, usually of several trained observers, well reinforced by amateur enthusiasts. The stations are chosen for the most part in North Carolina, Georgia, and eastern Alabama; in fact they are probably less widely distributed than they should be. Given only good weather, valuable results seem certain.

Popular interest in the eclipse and its results is evidently considerable. In view, however, of the importance, beauty, and rarity of the phenomenon, this interest ought, much more frequently than seems now to be the case, to take the form of planning to be present in person in the path of totality.

Mr. J. Lunt, Proceedings of the Royal Society No. 425, describes experiments which led him to ascribe certain lines in some of the helium stars to silicon. Like Sir Norman Lockyer he found these lines given off by vacuum tubes under a strong disruptive spark, and traced them to silicon derived from the glass of the tubes. In experiments with silicon tetrafluoride the differences in the behavior of silicon under different circumstances of discharge were exhibited in a striking

manner.

Professor Campbell (Astrophysical Journal, March) finds a variable velocity in the line of sight for ß Herculis. The period of the variation is unknown, but seems to be long.

In the Astronomische Nachrichten, No. 3629, Dr. K. Schwartzschild publishes a modification of the method of Professor Lehman Filbés for the computation of the orbit of a spectroscopic binary, by which the labor of the process is abridged.

Publications of Sir William Huggins' Observatory, Vol. I (William Wesley and Son, London) contains Sir William and Lady Huggins' Atlas of Representative Stellar Spectra from A 4870 to λ 3300. The volume opens with a short history of the Observatory, and contains, with the Atlas, a discussion of the evolutional order of the stars and the interpretation of their spectra.

In the Astrophysical Journal for March Professor Campbell gives the theory of the velocity of the Moon in the line of sight. As Venus and Mars are not always available to test the accuracy of measures of radial velocity it is sometimes desirable to obtain spectrograms of the Moon for the purpose. The distance, place of observation to Moon plus Moon to Sun, the change of which is the effective radial velocity of the Moon, may vary at a rate aimost as great as two kilometers per second. This motion is divided into several parts, the expression for each of which is so arranged as to be easily computed from data given in the Nautical Almanac. In an example Professor Campbell finds for the computed velocity + 1.14 kilometers for second, and for the measured velocity +1.46 km. per second.

In his annual report President Eliot of Harvard University states that Mrs. Fleming, whose name appears in the University catalogue as Curator of Astronomical Photographs, is believed to be the first woman who has held an official position in Harvard University.

The February number of the Monthly Notices of the Royal Astronomical Society contains the annual report of the Council. The Proceedings of Observatories contain, in a number of cases, reference to spectroscopic work. At the Cape of Good Hope the McClean photographic equatoreal has been used with the slit spectroscope for the study of star spectra, yielding the discovery of oxygen and of silicon in certain stars; the object-glass has now, however, been returned to the maker for correction. At Cambridge the work on star spectra with the Bruce spectroscope has been brought to a conclusion. At Stonyhurst a study of the Sun with a grating spectroscope has shown about the same degree of solar activity in 1899 as in 1898; also, the stellar spectrograph has been used to continue the investigation of possible changes in certain selected stars. At Wolsingham the search for stars with remarkable spectra has been continued with

success.

Of the summary of progress of astronomy during the year spectroscopic work is the subject of about one-fourth. The advance in stellar spectroscopy is summarized in a compact article occupying four pages, while two pages are devoted to a review of Sir William and Lady Huggins' Atlas of Representative Star Spectra.

Mr. Wright (Astrophysical Journal, March) has computed the orbit of the spectroscopic binary x Draconis from the results of 28 plates obtained with the Mills spectrograph of the Lick Observatory. For the projection in the line of sight of the major axis he finds 62,000,000 kilometers (39,000,000 miles), with a probable error of 400,000 km. (260,000 mi.); for the eccentricity 0.423, with probable error 0.006; and for the period 281.8 days, with probable error 0.7 days. The spectrum of x Draconis, resembling that of Procyon, with the Hy line of hydrogen well defined and the metallic lines sharp and well separated, was very suitable for measurement.

The death of Miss Catherine W. Bruce removes a very liberal friend of astronomical science, by whose ready and well directed financial aid the construction of much important spectroscopic and photographic apparatus and the prosecution of many valuable researches have been made possible.

PLANET NOTES FOR MAY.

H. C. WILSON.

Mercury is morning star, but too close to the Sun to be observed. At the time of the total eclipse Mercury will be just a little way west from the Sun as shown upon the eclipse chart No. 3, given in this number of POPULAR ASTRONOMY. It will doubtless be visible during totality of the eclipse and observers not in the path of totality might well spend some time in looking for the planet at the time of maximum eclipse. Mercury will then be so near superior conjunction that its disc will be fully illuminated and if those markings which Mr. Lowell's observers at Flagstaff saw so plainly are ever to be seen by others this should be the time. It is true Mercury will be on the farther side of the Sun and and its disc will be small, yet this would only reduce the size of the markings by one-half. For those, therefore, whose time is not occupied with the study of the corona and who have the use of telescopes with apertures of six inches and up

BAST HORIZON

wards, it may be well worth the while to study this planet carefully. Mercury
will reach superior conjunction on the morning of May 30, being very near peri-
helion at the same time, and after that will be evening star.

SOUTH HORIZON

Venus has just passed greatest elongation east from the Sun and will this month turn in toward the line joining Earth and Sun. The phase of Venus is now like that of the half Moon and will decrease gradually during the month. The planet, however, will continue to rapidly approach the Earth so that its brilliancy will still increase up to the first of June. Venus, the Moon, the Pleiades and the Hyades made a very pretty group in the western evening sky on

April 2. Venus will be in conjunction with the Moon again on May 2 but the Pleiades and the Hyades will be far down toward the west at that time. Again on May 31 there will be another conjunction of Venus and the crescent Moon.

Mars is morning star about 22° west from the Sun, declination 6° north. Its angular distance from the Sun and its northern declination will steadily increase throughout the summer and so the planet will come into more and more favorable position for observation. Mars will be in conjunction with Mercury on May 3, Mars being 2° north of Mercury. At the time of the total eclipse of the Sun, May 28, Mars will be near the meridian toward the south, and will no doubt be visible to the naked eye at the time of totality.

Jupiter will be at opposition May 27 and so may be best observed during the two hours before and after midnight.

Saturn may be observed between midnight and morning, being seen low in the south or southeast, according to the hour of observation, in the constellation Sagittarius.

Uranus is near Jupiter, in Scorpio, and may be observed at the same hours. Neptune is now low in the west in the evening, in the constellation Taurus, and practically out of position for observation for the remainder of this year.

NOTE.-In. denotes ingress; Eg., egress; Dis., disappearance; Re., reappear

ance; Ec., Eclipse; Oc., occultation; Tr., transit of the satellite; Sh., transit of the shadow.

I.

II.

Jupiter's Satellites for May.

Phases of the Eclipses of the Satellites for an Inverting Telescope.

No Eclipse.

41

I

•2

4'

I'

2. 3

4'

I

4'

'3

I

04

3'

3

I'

2.

4.

•2

2

2

$3