six to more than one hundred. In ARGELANDER'S Durchmusterung, the average number is 15.2, in SCHOENFELD'S it is 18.5, and in the Cordoba D. M. (-22° to -42°) it is 56.1.-Abstract of a paper in the Monthly Notices R. A. S., Vol. LVII, p. 297.

INTERNATIONAL CATALOGUE OF FUNDAMENTAL STARS.

In May, 1896, a Conference was held at Paris at the invitation of the Bureau des Longitudes, to consider a plan for the formation of a fundamental catalogue of standard stars for the ephemerides published in France, England, Germany, and America. The personnel of the Conference was Messrs. AUWERS (Germany), BACKLUND (Russia), BAUSCHINGER (Germany), CHRISTIE (England), DOWNING (England), GILL (Cape of Good Hope), LOEWY (France), NEWCOMB (United States), TISSERAND (France). M. FAYE (France) acted as President, and Messrs. v. d. S. BAKHUYSEN (Holland) and TREPIED (France) served as Secretaries. The conclusions of the Conference were adopted with practical unanimity. The most important were as follows: For the fundamental catalogue, the equinox should be determined solely from observations of the Sun, excluding those of Mercury and Venus. The equinox of Professor NEWCOMB'S system (N1) in Vol. I of the Astronomical Papers of the American Ephemeris was adopted.* In view of the uncertainty that still exists with regard to the numerical value of the personal error depending on magnitude, which affects the R. A., it was decided that corrections for such errors should not be applied. But as the existence of such (small and systematic) errors is undoubted, the Conference considered that observatories should make researches to fix their amounts. Professor NEWCOMB was entrusted with the duty of fixing the values of the precessions to be employed. The Conference decided to adopt the following constants: Nutation, 9".21;† Aberration, 20".47; Solar Parallax, 8".80.S It was decided that in the reduction of mean places of stars to apparent, the term of short period in R. A. (f') depending on twice the Moon's longitude should be omitted for both polar and equatorial stars.

From the adopted solar-parallax and the NEWCOMB-MICHELSON value of the velocity of light there results 20".467 ± 0.012.

Dr. GILL'S determination (heliometer) 8".802 ± 0.005.

Professor NEWCOMB was entrusted with the duty of preparing a provisional fundamental catalogue, which is to be finished during 1896. This catalogue is to contain about 1000 fundamental stars. The Conference laid down various other principles on which the catalogue should be constructed which are not mentioned here. It also expressed the hope that a scheme of international co-operation might be established for the calculation of the perturbations and ephemerides of the minor planets (of which there are now more than 400). The opinion was also formally expressed that a first-class reversible meridian-instrument, suitable for fundamental work, should be erected at one of the southern observatories. The changes of astronomical constants, as recommended by the Conference, are to take effect in the ephemeris for 1901. "There appears to be every reason to expect that the catalogue will be ready in good time, and that astronomers may look forward to the inauguration of a new era in the history of astronomical ephemerides at the commencement of the twentieth century."-Abstract of a paper by Dr. DOWNING in the Monthly Notices R. A. S., Vol. LVII, page 299.

PROBABLE ERROR OF A SINGLE OBSERVED POSITION IN SOME FREQUENTLY USED CATALOGUES AND COLLECTIONS OF STARS.

The probable accidental error of an observed place, depending on a single observation, in the following catalogues, etc., is (approximately) as follows:

R. A. (Equator). Decl.

Bonn Observatory (Vol. VI; stars 9th magnitude) .06

Grant's Glasgow Catalogue

0.6

(Vol. VI; stars 9.2 and 9.3) - .07

0.8

Bond's Zones (H. C. O. Vol. II)

0.8

Schjellerup's 10,000 stars

Lamont's Zones (re-reduced in Munich Annals, II) .08

0.9

Harkness' Gilliss Southern Zones

0.9

.04

Weisse's Bessel's Zones, I

I. I

.16

Göttingen (Klinkerfues Schur, 6900 stars)

1.4

.10

Argelander's Southern Zones (Oeltzen)

1.4

.12

Weisse's Bessel's Zones, II

1.4

Cincinnati Observatory (4050 stars)

Cape (Photographic) Durchmusterung

1.8

.27*

Lacaille (B. A. A. S.)

2.6*

Section II, Bonn Durchmusterung

66

ADDENDUM TO DR. MARTH'S ARTICLE ON PAGE 76.

9 33 29.5

16.40+1.15

-5.25-2.61 908.6

18.45

16.42+1.15

-5.26-2.60 908.6

18.45

1895, July 30

31

+6.69+7.51 929.4

10.16

34.63 +0.91

Oct. 10 16 2 2.2

NOTICE TO MEMBERS.

Owing to a misunderstanding, an essential part of the manuscript of the present number was not received until April 10th, which accounts for the delay in the issue.

THE COMMITTEE ON PUBLICATION.

* Probable errors of a printed catalogue-place.

RECENT OBSERVATIONS OF THE SPECTRUM OF MARS, BY W. W. CAMPBELL.

"In the year 1894, I described for the Chronicle my observations of the spectrum of Mars, and stated the conclusions to be drawn from them concerning the presence of atmosphere and water on that planet. The observations were made by visual methods entirely. In the spring of 1895 and the winter of 1896-97, I repeated the observations, making them by photography. Professor KEELER of the Allegheny Observatory (formerly of the Lick Observatory), recently wrote me that he also had observed the spectrum of Mars photographically in the last few months, and I have his permission to describe his results along with my own. Our work has an important bearing on the question of Mars' atmosphere and the conditions of life on that planet, and I take this opportunity of making it public. ***

"The problem was attacked in the years 1862-77 by HUGGINS, JANSSEN, VOGEL, and MAUNDER. All came to the conclusion that the spectroscope was able to detect evidence of atmosphere containing water-vapor. Their results supported the popular side of the question, and were accepted without reserve. Their observations were nearly all made under extremely unfavorable circumstances: with Mars near the horizon, with small telescopes, at stations near sea level and in very moist localities. I feel sure that the observers themselves would now be willing to say that much of their evidence was very discordant, and in some points it was erroneous. A case in court, based on similar evidence, would be dismissed, with costs levied on the plaintiff.

"While I believed that the early observations, though weak and discordant, were essentially correct, it seemed to me well worth while to repeat them at Mt. Hamilton, on account of the favorable circumstances of position and climate existing here. Among the advantages existing here may be mentioned: 1. A more powerful telescope and spectroscope. 2. The altitude of the observatory, eliminating the lower 4200 feet of atmosphere and its aqueous vapor. 3. The southern location of the observatory and the northern position of Mars in 1894, bringing the planet nearer the zenith. 4. The very dry air existing here in the early summer. With these and other favorable circumstances, I expected that a confirmation of previous results would be a simple and easy matter. Accordingly, I compared the Martian

and lunar spectra on several nights in 1894, when our atmosphere was remarkably dry, and the two bodies were at equal altitudes above the horizon. At all times the spectra of the two bodies appeared to be identical in every respect. The oxygen and aqueous vapor lines were stronger when the Moon and planet were near the horizon than when they were near the zenith, for the obvious reason, that in the lower positions the rays of light traversed the greater depth of our atmosphere. In fact, an increase of twenty-five to fifty per cent. in the length of path in our atmosphere seemed sufficient to change the spectrum appreciably.

"The conclusions to be drawn from the observations are very simple, yet they have been widely misunderstood. They are: 1. The observations furnish no evidence of the existence of a

Martian atmosphere containing aqueous vapor. 2. They do not prove that Mars has no atmosphere, nor do they even suggest that idea. They simply set a limit to the possible extent of the atmosphere, or, rather, to the quantity of oxygen and aqueous vapor contained in it. The light coming to us from Mars has been reflected from the planet's surface, or from the inner strata of its atmosphere, and has, therefore, passed twice, either completely or partially, through its atmosphere. If an increase of twenty-five to fifty per cent. in the length of path of the rays in our atmosphere changes the spectrum appreciably, the Martian atmosphere should have been detected, if it is one fourth as extensive as ours. 3. We know, from the waxing and waning of the polar caps with the advent of winter and summer, respectively, that Mars has some atmosphere and some vapor analogous to our water-vapor, but we do not know how much. They do not seem to exist in sufficient quantities to be detected by spectroscopic methods; that is, they do not seem to be more than one fourth as extensive as on the earth, and they may be considerably less.

"As soon as my 1894 results were published, Messrs. HUGGINS and VOGEL repeated their observations of 1867 and 1873, respectively. Both were very positive in the early years that Mars' atmosphere and aqueous vapor were very easy to detect, and must, therefore, be of great extent. They were able, in 1894, to confirm their early work in some points, but in others they were not. This is not the place to make a scientific criticism of scientific results, but it should be stated that at the points in