86 COSMOS. 



which two satellites of Uranus have been again distinguished. 

 The new colossal telescope of Lord Rosse has an aperture of 

 six feet, and is fifty-three feet in length. It is mounted in the 

 meridian between two walls, distant twelve feet on either 

 side from the tube, and from forty-eight to fifty-six feet in 

 height. Many nebulse, which had been irresolvable by any 

 previous instruments, have been resolved into stellar swarms 

 by this noble telescope; while the forms of other nebula) 

 have now, for the first time, been recognized in their true 

 outlines. A marvellous effulgence is poured forth from the 

 speculum. 



The idea of observing the stars by daylight with a tele- 

 scope first occurred to Morin, who with Gascoigne (about 1638, 

 before Picard and Auzout) combined instruments of measure- 

 ment with the telescope. Morin himself says, 38 " It was not 

 Tycho's great observations in reference to the position of the 

 fixed stars, when, in 1582, twenty-eight years before the in- 

 vention of the telescope, he was led to compare Venus by day 

 with the sun, and by night with the stars," but " the simple 

 idea that Arcturusand other fixed stars might, like Venus, when 

 once they had been fixed in the field of the telescope before 

 sunrise, be followed through the heavens, after the sun had 

 risen, that led him to a discovery which might prove of impor- 

 tance for the determination of longitude at sea." No one was 

 able before him to distinguish the fixed stars in the presence of 

 the sun. Since the employment, by Homer, of great meridian 

 telescopes in 1691, observations of the stars by day have 

 been frequent and fruitful in results, having been, in some 

 cases, advantageously applied to the measurement of the 

 double stars. Struve states 88 that he has determined the 

 smallest distances of extremely faint stars in the Dorpas 



* Delambre, Hist, de VAstron. moderne, t. ii. p. 255. 

 a Struve, Mens microm. p. xliv 



