170 CONSTRUCTION OF LAROE TELESCOPE LENSES. 



aperture, poured at Jena, ground in Munich (1896), and costing 

 55,000 marks. 



The objective of the Dorpat refractor, with 25 centimeters aperture, 

 which, as it came from the master hand of Fraunhofer, was regarded 

 as a wonder of the world, can scarcely be counted among the large 

 telescopes to-day, for already more than 100 exceed its dimensions. 

 It would lead too far to mention them all, but it is not out of place 

 to remark that there is work of great value also for the smaller 

 lenses. Interesting studies of the features of the planets have been 

 made even in recent times with smaller instruments. Thus Schiapa- 

 relli, the famous discoverer of the so-called Martian canals, made his 

 earlier valuable observations with an 8-inch telescope, which would 

 now be classed as a minor instrument. In planetary oljservation the 

 advantages of fine optical definition, together with good atmospheric 

 conditions, combined with practiced eyes, are of more consequence than 

 high power or great light-gathering capacity. The advantages of 

 the largest instruments lie in the possiV^ilities they afford of observing 

 the fainter fixed stars and nebula" which lie at immeasurable distances. 



