THE DIAMETERS OF THE STAKS. ] 



By A. Danjon, 

 Astronomer at the Strasbourg Observatory. 



[With 1 plate.] 



Stellar astronomy is now taking its place definitely in the ranks of 

 sciences. For 20 to 30 years the census of the starry heavens grew, 

 star after star, nebula after nebula, without any definite bond, any 

 generalization, any law emerging showing the connections existing 

 among their number. Astronomers seemed yet in the dark as to 

 any general plan of the universe. Similarly before Ptolemy and 

 Hipparchus, except for the existence of the planets, the plan of the 

 solar system was not known. The astronomers of Alexandria made 

 their names forever illustrious in showing that the planets were 

 subject to laws. They gained the first approximation to the plan of 

 the solar system. True, it fell to the lot of others, of Kepler, of New- 

 ton, to give a more thorough solution of the problem and a deductive 

 status to planetary astronomy. But without their predecessor's 

 steps, how halting would have been their progress. 



The solving of the problems of sidereal astronomy began when 

 physics produced the appropriate tools. The elder Herschel had 

 marked out the way, helped by his great ingenuity but handicapped 

 by paucity of instrumental means. The American school of astrono- 

 mers has put on foot the work which we of to-day admire both for 

 its rich promise and the germs of truth it contains. Truly hypo- 

 thesis plays a preponderant part in the interpretation of the observa- 

 tions. We are yet far from the completion of a magnificent logical 

 structure such as planetary astronomy has gained. A mathema- 

 tician would be ill at ease before the numerous publications which 

 bring us the echo of the discoveries gleaned from the stellar universe. 

 At present astronomers are garnering facts; the near future may 

 bring the Newton or the Kepler who will place them in their proper 



! At a general assembly of the Societe Astronornique de France Professor Miclielson 

 described his method of measuring stellar diameters. A survey of some related subjects 

 Is useful as an introduction to his work. 



Translated by permission from L'Astronomie, November and December, 1921. 



101257—22 12 165 



