ering, Campbell and Frost (directors of the Harvard, Lick and Yerkes observatories) were elected chairmen for the three days of the meeting, and Messrs. Puiseux (of Paris), Konen (Münster) and Adams (Mt. Wilson), secretaries of the meeting. All formal business was announced in English, French and German, and the three languages were used in the discussions, which emphasized the international character of the gathering.
Dr. Hale made the opening address. He welcomed the visitors to the observatory, and described the work in progress there, dwelling especially on the recent discoveries that sun-spots are the centers of a vortical movement in the upper layers of the solar atmosphere, and the seat of strong magnetic fields, and describing the new "tower telescope," of 150 feet focal length, mounted vertically on a tower, every member of whose framework is completely surrounded by that of an outer tower, protecting it from vibration and other disturbances, while the spectroscopic apparatus, of 75 feet focal length, is in a deep well under the tower, effectually protected from changes of temperature and other perturbations.
The report of the committee on standard wave-lengths was presented by Professor Kayser (Bonn), and it was voted that when three independent measurements by the interference method of the lines of the iron arc are available, the arithmetical mean of the three shall be adopted as international standards of the second order (Michelson's determination for the red cadmium line being the primary standard). Standards of the third order are to be determined by interpolation between these and a complete system of very exact reference points throughout the spectrum thereby obtained.
Dr. Abbot, of the Smithsonian Astrophysical Observatory on Mount Wilson, lectured that evening on the solar constant of radiation, and presented a committee report dealing with the same subject on the following morning. After correcting for the absorption of heat in passing through our atmosphere (a very difficult problem, now in a fair way toward solution) the heat received from the sun appears to be slightly less than two gram-calories per square centimeter per minute. The Mount Wilson observations, however, show changes of short and irregular period (a few days) which exceed the errors of observation. It is exceedingly desirable to establish a second station some distance away (say in Mexico) where simultaneous observations may be made, to determine whether these changes are of solar or atmospheric origin.
The report of the committee on the spectra of sun-spots was presented by Professor Fowler (South Kensington). The principal feature of interest was the remarkable constancy, even in small details, of the spectrum shown by different spots.
On the second evening (Thursday) Professor Kapteyn (Groningen) lectured on "Star-streams among Stars of the Orion Type," showing that in a large region of the southern sky (including Scorpio, Centaurus and the Southern Cross) 85 per cent, of the stars of this spectral type (supposed to be the hottest) are moving together in space, their actual motions being very nearly equal and parallel; while in Perseus and neighboring constellations 95 per cent, of the stars of the same type have a similar common drift, but of different magnitude and direction. The velocity of these drifts can be found from spectroscopic observations, which makes it possible to determine the distances of these remote stars, which in some cases appear to be as great as 500 light-years—far beyond the possibility of direct measurement.
On Friday reports from committees on solar rotation and on spectroheliographic work were presented, and, the regular business being at an end. the question of tho extension of the work