THE HlJ^TORY f)F THE TELESCOPE. 103 



oarly aoo nf 39, he had not only l^ionglit the nchromatic telescope to a 

 (U'jiice of ojjtical ]K'iieetioii which niade it a rival of the most ])<)werful 

 of the relh'ctor ty])«', and so far improved its method of inouiitiiig', that 

 his system has replaced all others; but he also made some capital dis- 

 co\eries in the domain of i)hysical optics. His great achievement was 

 the c(mstrnction of an achromatic telescoi)e U.G inches in diameter, 

 w ith which the eldci- Srruve made at Dorpat his remarkable series of 

 discoveries and measurement of donl)le stars. The character of 

 Struve's woik demonstrates the excellence of the telesco])e, and shows 

 ns that it is to be i-anked as the ecpial of all but the very best of its 

 l>redecessors. Indeed, it may lairly l)e concluded that not more than 

 one or two telescopes, and those made and used by Ilerschel, had ever 

 been of .i^reater })ower, while in convenience for use the new refractor 

 was vastly superior. 



For a long time Fraunhofer and his successors. Merz and Mahler, 

 from whom the great telescopes of Pulkowa and of the Harvard Observ- 

 atory were procured, icmained unri\ ailed in this tield of optics. But 

 they have been followed In' a number of skillful constructors whose 

 products have, since the middle of the century, been scattered all over 

 the world. In ( Jermany, Hteinheil and Schi(>der: in France, Canchois, 

 JMartin, and the lleniy brothers; in England, Cook and (iriil)!); and in 

 this country the ('larks and Brashear, h-<v<' eacii jjroduced one or more 

 great telescoi>es which has rendered his name tamiliar to all readers of 

 astnmomical history. ( )f these the Clarks, father and son, have beyond 

 a doubt won the first i)lace, whether determined by the character of 

 the disco\eries made by nu'ans of their instruments or by the fact that 

 the two most ])Owerful telescopes in existence were made by them, 

 namely, the new refractor of .">() inches in diameter, at Pulkowa, and tlu' 

 gicnt rt^ractor of.'] feet diameter, of the Lick ()l)servatory in ralifornia. 

 'i'lie most uotal>le discox'ciies made witii their telescopes are the satc^l- 

 lites of Mars and tiie com[)anion to Sirius; but besides these there is a 

 long list of double stars of tluMuost difticult character discovered by 

 the makers themselves, by Dawes, in I'^nglaud, by Ibiinham, in our 

 own country, and by a nund)ei' of other observers. 



W(! ought not to terminate our review of the development of the tel- 

 escope without a reference to the parallel develoi)ment of the mounting 

 of great telescopes. Indeed, <lid this not lead us too far from the im- 

 mediate aim in view, we might iind a. great deal of interest and Ix^ 

 brought info agre<'able contact with sonu'of the cleverest nu'chanicians 

 and engineers of two ceiituiies by tracing its course. A\e should 

 meet with lluygluMis, ;is the inventor of the aerial telescope, and per- 

 hajts consider the claims of his c(>nfeiuporar\ , K'obeit Ilook, as a rival 

 inventor, for we may be sure that nothing which brings us to a study 

 of that curious and able philosopher wouhl tail to possess in ter(^st. We 

 should find ilerschel confrcuifed with the problem as to how he should 

 use his gieat 4()-foot telescoi>e. and the study of his solution would 



