620 



NATURE 



{Oct. 25, 1883 



fully, generally in the words of the author, including dis- 

 cussions as well as original observation ; so, as the 

 author points out, the admirable re'sumSs of Liaponoff, 

 Struve, D'Arrest, and others are available for immediate 

 reference. 



Although Cysat of Lucerne discovered the nebula, it 

 was not the first discovered, that in Andromeda having 

 been noticed by Abdul Rahman al Sufi, A.D. 950, nor 

 were Cysat's observations of much value. The observa- 

 tional work really dates from 1656, when Huyghens inde- 

 pendently observed it, and recorded roughly, as we have 

 said, its shape and the included stars. After all we must 

 not be too hard on the early observers, for, according to 



Arago, Huyghens' telescopes of 2\ inches diameter were 

 12 and 23 feet long, power 48 ; drawing at the telescope, 

 therefore, was almost out of the question. This notable 

 observation did not long escape our own keen-eyed 

 Hooke, who added to the triad of stars in the central 

 part of the nebula two others, and henceforward the 

 little stellar group has been called the "trapezium," and 

 is a test object dear to all amateurs. Hooke's telescope 

 was 36 feet long, aperture 3$ inches. Huyghens, in his 

 later observation (1694), also caught the fourth star. 



After this time the nebula and the number of its in- 

 cluded stars grew and grew with every increase of optical 

 power. 



Fig. 1. — The Great Nebula in O.ion (from a photograph by Mr. A \. Common). 



The observations of Mairan (1731), Long (1742), Le 

 Gentil (1758), Messier (1771), and Sir Wm. Hershel 

 (1744-1811) follow next, the latter especially giving con- 

 siderable attention to the nebula with his gigantic reflec- 

 tors ; and indeed it may be said he was the first to 

 seriously study it, and among the results of his observa- 

 tion was the statement that the nebula had undergone 

 changes during the time he had been studying it. The 

 three points insisted upon by Herschel are carefully dis- 

 cussed by Holden, with the result that he considers none 

 of them to be established. 



Interpolated between the observations of Sir Wm. 

 Herschel and his son (1824) are those of Schrceter 



(1794-98), Lefebvre (1799), Bode (1800), and Flaugergues 

 (1802). 



In Sir John Herschel's first memoir the accepted no- 

 menclature is established ; this is partly shown in the 

 annexed sketch. 



Like his father Sir John Herschel discussed the ques- 

 tion of change. " To the reader who has never viewed 

 this object through powerful telescopes, but who is 

 familiar with the various representations which have 

 from time to time been made of it (including my own 

 of 1824), the number and complexity of the various 

 branches and convolutions now first exhibited, and the 

 different aspects under which the portions best known 



