318 ANNUAL OF SCIENTIFIC DISCOVERT. 



tected, having escaped notice on many occasions when its position 

 had been under examination with the same telescope and powers. 

 Hence I was induced to hint at its probable variability in a note upon 

 the nebula, published in No. 838 of the Astronomische Nachrichten. 

 The suspicion is fully confirmed ; the star has diminished to the 

 twelfth magnitude, either simultaneously with, or soon after, the ap- 

 parent extinction of the nebula. 



M. LeVerrier states that on the night of January 26th, 1862, the 

 sky being very clear at intervals, the Paris equatorial, which has an 

 object-glass twelve French inches in diameter, was directed to the 

 place of the nebula, but, notwithstanding stars of an extremely faint 

 class were visible in its immediate neighborhood, not the slightest 

 trace of it could be perceived. The star which d' Arrest and Mr. 

 Hind had repeatedly noted, of the tenth magnitude, and almost 

 touching the nebula, had dwindled down to the twelfth ; so that tel- 

 escopes which would have shown it well between 1852 and 1856 

 would not at present afford a glimpse of it. From the fact that M. 

 Chacornac saw the nebula in forming a chart of the stars in that 

 region in 1854, and did not remark it while reconstructing the same 

 in 1858 with a much more powerful instrument, there is reason to 

 infer that the disappearance took place in 1856 or the following year. 



How the variability of the nebula and a star closely adjacent is to 

 be explained, it is not easy to say in the actual state of our knowl- 

 edge of the constitution of the sidereal universe. A dense but invis- 

 ible body of immense extent, interposing between the earth and them, 

 might produce effects which would accord with those observed ; yet 

 it appears more natural to conclude that there is some intimate con- 

 nection between the star and the nebula, upon which alternations of 

 visibility and invisibility of the latter may depend. If it be allowa- 

 ble to suppose that a nebula can shine by light reflected from a star, 

 then the waning of tlie latter might account for apparent extinction 

 of the former ; but in this case it is hardly possible to conceive that 

 the nebula can have a stellar constitution. It is at least curious that 

 several variable stars have been detected in the region of the great 

 nebula, in Orion; that in 1860 a star suddenly shone out in the mid- 

 dle of the well-known nebula Messier 80 (about half-way between 

 Antares and Beta in Scorpio), which vanished in a few days, and that, 

 as first remarked by Sir John Herschel, ail the temporary stars, with- 

 out exception, have been situated in or near to the borders of the 

 Milky -Way the star cluster or ring to which our system of sun and 

 planets belongs. In the latter class are included the memorable star 

 of B. c. 134, which led Hipparchus to form his catalogue of stars, and 

 those which blazed forth in 1572 and 1604, in the times of Tycho 

 Brahe and Kepler. 



Prof. Secchi, the well-known Roman astronomer, also informs Mr. 

 Hind that he has been unable to detect any traces of the nebula with 

 the powerful telescope at his command, and favored by the clear sky 

 of his locality. 



M. d' Arrest, since the above statement of Mr. Hind, also announ- 

 ces that he has detected a similar change in a nebula discovered by 

 Mr. Tuttle in February, 1859, and one discovered by Mr. Temple in 

 October of the same year. He regards a change of lustre in these 



