170 CONSTRUCTION OF LARGE TP:LESC0PE LENSES. 



aperture, poured at Jena, fjronnd in jNIunich (189G), and costing 

 55,000 marks. 



The objective of tlie Dorpat refractor, Avith 25 centimeters ai)erture, 

 which, as it came fi-om the master hand of Fraunhofer, was regarded 

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

 telescoj^es to-day, for already more than 100 exceed its dimensions. 

 It would lead too far to menti<m 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 S(liia])a- 

 rclli, the famous discoverer of the so-called Martian canals, made liis 

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

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

 advantages qf 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 possibiliti(>s they afford of observing 

 the fainter fixed stars and nebulae which lie at immeasurable distances. 



