THE PROBLEMS OF ASTRONOMY. 91 



most favorable conditions, they can not lose sight of the fact that the 

 ablest and most experienced observers are liable to error when they 

 attempt to delineate the features of a body 50,000,000 or 100,000,000 

 miles away through such a disturbing medium as our atmosphere. Even 

 on such a subject as the canals of Mars doubts may still well be felt. 

 That certain markings to which Schiaparelli gave the name of canals 

 exist, few will question. But it may be questioned whether these mark- 

 ings are the fine, sharp, uniform lines found on Schiaparelli's map and 

 delineated in Mr. Lowell's beautiful book. It is certainly curious that 

 Barnard at Mount Hamilton, with the most powerful instrument and 

 under the most favorable circumstances, does not see these markings 

 as canals. 



I can only mention among the problems of the spectroscope the ele- 

 gant and remarkable solution of the mystery surrounding the rings of 

 Saturn, which has been effected by Keeler at Allegheny. That these 

 rings could not be solid has long been a conclusion of the laws of 

 mechanics, but Keeler was the first to show that they must consist of 

 separate particles, because the inner portions revolve more rapidly than 

 the outer. The question of the atmosphere of Mars has also received 

 an important advance by the work of Campbell at Mount Hamilton. 

 Although it is not proved that Mars has no atmosphere, for the exist- 

 ence of some atmosphere can scarcely be doubted, yet the Mount Ham- 

 ilton astronomer seems to have shown, with great conclusiveness, that 

 it is so rare as not to produce any sensible absorption of the solar rays. 



I have left an important subject for the close. It belongs entirely to 

 the older astronomy, and it is one with which I am glad to say this 

 observatory is expected to especially concern itself. I refer to the 

 question of the variation of latitudes, that singular phenomenon 

 scarcely suspected ten years ago, but brought out by observations in 

 Germany during the past eight years, and reduced to law with such 

 brilliant success by our own Chandler. The North P.ole is not a fixed 

 point on the earth's surface, but moves around in rather an irregular 

 way. True, the motion is small ; a circle of 60 feet in diameter will include 

 the pole in its widest range. This is a very small matter so far as the 

 interests of daily life are concerned ; but it is very important to the 

 astronomer. It is not simply a motion of the pole of the earth, but a 

 wabbling of the solid earth itself. No one knows what conclusions of 

 importance to our race may yet follow from a study of the stupendous 

 forces necessary to produce even this slight motion. 



The director of this new observatory has already distinguished him- 

 self in the delicate and difficult work of investigating this motion, 

 and I am glad to know that he is continuing the work here with one of 

 the finest instruments ever used in it, a splendid product of American 

 mechanical genius. I can assure you that astronomers the world over 

 will look with the greatest interest for Professor Doolittle's success in 

 the arduous task he has undertaken. 



