126 PROGRESS IN ASTRONOMY. 



and active observatories, and the careful and thorough teaching estab- 

 lished side by side with them, which enables numberless students to 

 use the various instruments, the United States in matters astronomical 

 fills the position occupied by Germany at the beginning of the century. 



In Europe special observatories have been established at Meudon, 

 Kensington, and Potsdam, so that new astrophysical inquiries may be 

 undertaken without interfering with the prosecution or extension of 

 the important meridional work carried on at Paris, Greenwich, and 

 Berlin. A large proportion of the observations made by the Lick and 

 Yerkes observatories in the United States has been astrophysical. 



One of the special inquiries committed to the charge of the Solar 

 Physics Observator}" at Kensington at its establishment by the British 

 Government had relation to the possibility of running home meteoro- 

 logical changes on the earth, especially those followed by drought and 

 famines in various parts of the Empire, to the varying changes in the 

 sun indicated by the ebb and flow of spots on its surface. With this 

 end in view observations of the sun were commenced in India and the 

 Mauritius to supplement those taken at Greenwich. At the same time 

 other daily observations of sun spots by a different method were com- 

 menced at Kensington. 



This kind of work was at first considered ideally useless; we shall 

 see later on what has become of it. 



IMPROVEMENTS IN TELESCOPES. 



The progress in astronomical science throughout the closing century 

 has naturally to a great extent depended upon the advances made both 

 in the optics of the telescope and the way in which they are mounted, 

 either with circles to record exact times and positions, or made to move 

 so as to keep a star or other celestial objects in the field of view while 

 under ol)servation. The perfection of definition and the magnitude of 

 the lenses employed in the modern instrument have been responsible 

 for many important discoveries. 



Ever since the telescope was invented — Galileo's lens was smaller 

 than those used in spectacles — men's minds have been concentrated on 

 producing instruments of larger and larger size to fathom the cosmos 

 to its innermost depths. 



At the beginning of this century we were, as we have seen already, 

 in possession of reflectors of large dimensions; Herschel's -i-foot 

 mirror, the instrument he was using in 1801, which had a focal length 

 of 10 feet, was capable of being employed with high magnifying 

 powers; and it was the judicious use of these, on occasions when the 

 finest of weather prevailed, that enabled him to enrich so extensively 

 our knowledge of the stellar and planetary systems. For the ordinary 

 work of astronomy, however, especially when circles are used, ref rac- 



