ASTRONOMY AND METEOROLOGY. 317 



invisible companion of no inconsiderable magnitude. This announce- 

 ment had hardly found its way into print, when Mr. Alvan Clark, of 

 Cambridge, Massachusetts, through the agency of a new achromatic 

 telescope (recently constructed by him), having an object-glass of 

 eighteen and a half inches in diameter, and an illuminating power ex- 

 ceeding by more than one-half any other achromatic in existence, 

 discovered an object near Sirius, hitherto unknown to astronomers ; a 

 discovery since verified by many astronomers in this country and in 

 Europe. It is somewhat difficult to assign a reason why the exist- 

 ence of this body has not been made known before, as it is readily 

 visible through powerful telescopes, even a few minutes after sunset. 

 It, however, remains to be seen whether it will have to be the hith- 

 \ erto invisible body disturbing the motions of Sirius. Mr. G. P. Bond, 

 in a communication to Silliman's Journal, says of it: It will require 

 one, or at the most two years to prove the physical connection of the 

 two stars as a binary system. For the present we know only that the 

 direction of the companion from the primary accords perfectly with 

 theory. Its faintness would lead us to attribute to it a much smaller 

 mass than would suffice to account for the motion of Sirius, unless we 

 suppose it to be an opaque body or only feebly self-luminous. 



DISAPPEARANCE OF NEBULA. 



One of the most mysterious and unlooked-for of recent phenomena 

 in the heavens is the discovery of a change of lustre, and even dis- 

 appearance of certain nebulas. The nature of these phenomena is 

 thus set forth in a recent statement published by Mr. Hind, the 

 well-known English astronomer. Towards the close of 1861, it was 

 announced by Prof, d' Arrest, of Copenhagen, that a nebula in the 

 constellation Taurus, which was discovered on the llth of October, 

 1852, had totally vanished from its place in the heavens. That one 

 of these objects, which the giant telescopes of the present day had 

 taught us to regard as assemblages of stars in myriads at immense 

 distances from the earth, should suddenly fade away, so as to be 

 quite imperceptible in powerful instruments, must, I think, have been 

 deemed a very improbable occurrence, even by many who are well ac- 

 quainted with the care and experience of the observer by whom the 

 statement was made. Since the date of M. d' Arrest's statement, 

 however, M. LeVerrier has obtained so strong a confirmation of its 

 accuracy that there is no longer room for supposing it to have origin- 

 ated in one of those errors of observation which every practical 

 astronomer knows will creep into his work in spite of all his precau- 

 tions. 



The nebula in question was situated in right ascension 4 hours 1 3 

 minutes 54.6 seconds, and north declination 19 II 7 37," for the be- 

 ginning of 1862. It was, therefore, about a degree and a half from 

 the star Epsilon in Taurus, in the group commonly known as " the 

 Hyades." Its diameter was about one minute of an arc, with a con- 

 densation of light in the centre ; or its appearance was that of a 

 distant globular cluster, when viewed in telescopes of insufficient 

 power to resolve it into stars. From 1852 to 1856 a star of the tenth 

 magnitude almost touched the edge of the nebula at its north-follow- 

 ing edge ; it was at first remarked on the night the nebula was de- 

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