368 



SCIENCE. 



[N. S. Vol. XVI. No. 401. 



which comes into view only at the times of 

 total solar eclipses— the sun's ' crown of 

 glory,' the corona— at present can be 

 studied for about an hour during a cen- 

 tury, if we estimate the time the astronomer 

 has been able to actually see the corona. 



But photography has here brought us 

 most satisfactory results. Many negatives 

 are now obtained at every eQlipse of the 

 sim, and these can be studied and measured 

 at leisure. At an observing station for a 

 total solar eclipse, the astronomer of fifty 

 years ago would be dumbfounded to see 

 how few and how small are the instruments 

 set aside for the eye observations. All the 

 large instruments and most of the observ- 

 ers' time are given to the photographic 

 work. How fortunate this is— for not only 

 can the originals be studied with great care, 

 but copies can be furnished to all astron- 

 omers the world over for inspection and for 

 comment. 



In the past the discovery of new planets 

 always excited a deep interest in the minds 

 of men. To-day we are so accustomed to 

 the discovery of new minor planets (some- 

 times as many as twenty-eight in one year) 

 that we pass them by without much notice. 

 You no doubt remember that the astron- 

 omers of the eighteenth century had great 

 faith in Bode's law. This law stated that 

 the planets were arranged in order of dis- 

 tance from the sun according to the num- 

 bers, 4, 7, 10, 16, 28, 52, etc. These numbers 

 were obtained by writing down the numbers 

 0, 3, 6, 12, 24, 48. All the numbers after 

 the second were obtained by multiplying the 

 preceding number by two ; and then adding 

 four to each result. Representing the 

 earth's distance as 10 the other numbers 

 represented very fairly the distances of the 

 other planets, but there was a break at 28. 

 No planets were known at the distance 2.8 

 times the earth's distance from the sun. 

 The law was so firmly believed in that in 

 the latter part of the eighteenth century a 



number of astronomers joined in the search. 

 They were dubbed the ' celestial police.' 

 The first fugitive planet was found by 

 Piazzi, January 1, 1801, an astronomer of 

 Sicily, who had not yet received notice of 

 his appointment on the force. 



Then the search was later taken up most 

 vigorously, and down to 1892 about 325 

 were discovered. But in the latter part of 

 the preceding year Dr. Wolf, of Heidelberg, 

 inaugurated the scheme of photographing 

 the heavens. He made his exposures in 

 duplicate, and for two or three hours. The 

 result was that if a minor planet was in the 

 field, as the telescope was guided by follow- 

 ing accurately a star, the planet's moving 

 caused a short dash to appear on the plate 

 instead of a round star image. 



The plates were measured and from these 

 measurements the astronomer covild deter- 

 mine whether the planet was new or an 

 old one. In carrying out this work Dr. 

 Wolf, Charlois of Nice, and others have 

 been so successful that, since November 28, 

 1891, the list of minor planets, mainly dis- 

 covered by photography, has increased to 

 nearly five hundred. Wolf 's work attracted 

 the attention of the late Miss Catherine 

 Wolfe Bruce, of New York City, who has 

 done so much for astronomy. Miss Bruce 

 gave Wolf the means to build a fine photo- 

 graphic outfit. The new apparatus he had 

 built in this country, and is now using with 

 the most eafeellent results. He has immor- 

 talized that noble, generous woman by 

 naming one of the planets Brucia. He 

 showed his appreciation of the work of the 

 Lick Observatory by giving the appellation 

 of California to the planet he discovered on 

 September 25, 1892, and he had previously 

 named another Chicago, after the city he 

 expected to visit during the Exposition of 

 1893. 



Photography has so rapidly increased the 

 number of these little planets that there has 

 been some serious discussion as to whether 



