2-jo THE POPULAR SCIENCE MONTHLY. 



our means of observation and as an example of how the standai-d of 

 such work has been gradually raised. It will be interesting to trace 

 in the same way the history of the Horseshoe Nebula in Sagittarius, 

 which, next to the great nebulosities of Orion and Andromeda, is the 

 most curious of these objects, and which perhaps as much as any 

 other deserves careful study. 



Its discovery dates back about a hundred years to the time of 

 Messier, the assiduous astronomer of the Observatoire de la Marine 

 at Paris ; it is No. 17 of his list, which comprises most of the brighter 

 and more remarkable nebula? of the northern sky. It was at this time 

 that Sir William Herschel, the famous astronomer of England, with in- 

 struments far superior in power to those of Messier, was forming his 

 great catalogues of the nebulge discovered in his " sweeps." Messier 

 wisely used his smaller instrument in the endeavor to obtain accurate 

 positions for those found by him, and he has left us monographic 

 studies of the Orion and the Andromeda nebula (" Memoires de 

 I'Academie des Sciences," IVZI and 1807), which are almost the first 

 trustworthy works of the kind, and which are the beginnings from 

 which sprang the elaborate drawings of Lassell, Rosse, Struve and 



Bond. 



s 



N 

 Fig. 1. J. Herschel, 1833. 



From the time of Messier to 1826, when Sir John Herschel pub- 

 lished his first figure of the Orion nebula, almost nothing was done 

 in this line of research ; but in 1833 a study of the Horseshoe Nebula 

 was published by Sir John Hei-schel, together with many other similar 

 drawings, in the "Philosophical Transactions" [see Fig. 1). This was 

 the first considerable and systematic attempt to accurately figure the 

 nebulae, and it doubtless turned the attention of astronomers generally 

 to this branch, the importance of which was manifest. If so many of 

 the fixed stars changed in brilliancy and in position, why should not 



