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THE POPULAR SCIENCE MONTHLY 



ering, Campbell and Frost (directors 

 of the Harvard, Lick and Yerkes ob- 

 servatories) were elected chairmen for 

 the three days of the meeting, and 

 Messrs. Puiseux (of Paris), Konen 

 (Minister) and Adams (Mt. Wilson), 

 secretaries of the meeting. All formal 

 business was announced in English, 

 French and German, and the three lan- 

 guages 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 ob- 

 servatory, 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 at- 

 mosphere, and the seat of strong mag- 

 netic 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 vibra- 

 tion 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 per- 

 turbations. 



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 interna- 

 tional standards of the second order 

 (Michelson's determination for the red 

 cadmium line being the primary stand- 

 ard ) . Standards of the third order 

 are to be determined by interpolation 

 between these and a complete system 

 of very exact reference points through- 

 out the spectrum thereby obtained. 



Dr. Abbot, of the Smithsonian As- 

 trophysical Observatory on Mount Wil- 

 son, 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 atmos- 

 phere (a very difficult problem, now in 

 J 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 exceed- 

 ingly desirable to establish a second 

 station some distance away (say in 

 Mexico) where simultaneous observa- 

 tions 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) lec- 

 tured on " Star-streams among Stars 

 of the Orion Type," showing that in a 

 large region of the southern sky (in- 

 cluding 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 constella- 

 tions 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 ob- 

 servations, 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 be- 

 yond the possibility of direct meas- 

 urement. 



On Friday reports from committees 

 on solar rotation and on spectrohelio- 

 graphic work were presented, and, the 

 regular business being at an end, the 

 question of the extension of the work 



