July 5, 1901.] 



SCIENCE. 



n 



values of the constants which we now pos- 

 sess, and with improvements in method 

 unknown one hundred years ago, which 

 cannot fail to add greatly to its useful- 

 ness. 



As time went on observations were con- 

 ducted with more or less regularity at va- 

 rious places, each observer or institution 

 acting independently of what was done else- 

 where. As a result, many stars were ob- 

 served over and over again, and others, 

 equally important, not at all. In 1866, 

 however, the Astronomische Gesellschaft 

 of Germany organized a systematic cam- 

 paign, having for its object the accurate cata- 

 loguing of all stars of the northern heavens 

 not fainter than the 9th or 9.5th magni- 

 tude. For this purpose the entire north- 

 ern heavens were divided into zones of about 

 5° in width, and thirteen different observa- 

 tories each undertook to observe one, or in 

 some cases two, of these zones, the work all 

 being done on a strictly uniform plan, so 

 that the results shall be homogeneous 

 throughout. This work has been in progress 

 for more than thirty years — somewhat de- 

 liberately at some places, it must be said, 

 but is now nearly completed. The plan 

 has since been extended to include southern 

 stars as far as the tropic of cancer. Mean- 

 while our own distinguished countryman, 

 Dr. B. A. Gould, as the result of fifteen 

 years' labor at Cordoba, Argentina, has 

 given us a similar catalogue of 73,160 stars 

 between the tropic of cancer and the south 

 pole. 



The great work, instituted by the Astro- 

 nomische Gesellschaft in 1865, is still unfin- 

 ished, yet an even more ambitious under- 

 taking was inaugurated fourteen years ago 

 by an international congress assembled at 

 Paris for that purpose. This calls for a 

 photographic survey of the heavens to be 

 participated in by a number of observa- 

 tories — eighteen have joined in the under- 

 taking — two sets of plates being taken. 



The first set are to have sufficient length 

 of exposure to give positions of all stars not 

 fainter than the eleventh magnitude. These 

 are to be measured and the resulting posi- 

 tiolas catalogued. When completed, this 

 catalogue will include between two and 

 three million stars. The second series of 

 plates is to have a longer exposure, sufficient 

 to show stars of the fourteenth magnitude 

 and will furnish charts of the heavens. 

 22,154 plates are called for and many 

 years will be required for its comple- 

 tion. The results already obtained show 

 that star positions may be obtained in 

 this way with an accuracy little if any- 

 thing inferior to the results of meridian 

 observation. 



The problem of the past history and 

 future destiny of the solar system has oc- 

 cupied much attention during the century. 

 Near its beginning Laplace had announced 

 his famous nebular hypothesis. For many 

 years it seems to have been taken for granted 

 that little if anything could be added to this 

 theor3^ In a general way it may be said 

 that it forms the foundation of whatever 

 has been developed in this direction. La- 

 place began with the sun already existing, 

 surrounded with an atmosphere of heated 

 vapor extending beyond the farthest planet. 

 This body revolved on its axis and grad- 

 ually shrunk as its heat was radiated into 

 space. The linear velocity of the outer 

 parts remaining constant, the angular veloc- 

 ity would constantly increase until in time 

 the centrifugal force became equal to the 

 centripetal when the central part separated, 

 leaving the equatorial part in the form of a 

 ring. This ring contained the material out 

 of which the outermost planet was formed. 

 Successive repetitions of the process pro- 

 duced the diiferent planets, and these in 

 turn produced satellites in the same manner. 

 The rings of Saturn were held to be almost 

 an unanswerable piece of evidence in favor 

 of the theory. Though, without doubt, the 



