ness and mystery. As in the case of some of the other species of these phenomena, so in this, the mind feels unable to form any definite or satisfactory conceptions on the subject. The following remarks of Sir J. Herschel comprise most of what can be stated, in the mean time, on this subject: "Whatever be their nature, they must be of enormous magnitude. One of them is to be found in the parallel of v Aquarii, and about five minutes preceding that star. Its apparent diameter is about twenty seconds.. Another, in the constellation Andromeda, presents a visible disk of twelve seconds perfectly defined and round. Granting these objects to be equally distant from us with the stars, their real dimensions must be such as would fill, on the lowest computation, the whole orbit of Uranus. It is no less evident that, if they be solid bodies of a solar nature, the intrinsic splendour of their surfaces must be almost infinitely inferior to that of the sun's. A circular portion of the sun's disk, subtending an angle of twenty seconds, would give a light equal to 100 full moons, while the objects in question are hardly, if at all, discernible with the naked eye. The uniformity of their disks, and their want of apparent central condensation, would certainly augur their light to be merely superficial, and in the nature of a hollow superficial shell; but whether filled with solid or gaseous matter, or altogether empty, it would be a waste of time to conjecture." In this description there is nothing which strikes the mind with such astonishment as the enormous magnitude of these planetary nebula. A globular body which would fill the orbit of Uranus would contain 24,429,081,600,000,000,000,000,000,000, or more than twenty-four thousand quartilions of solid miles. The solid contents of the sun is about 357,000,000,000,000,000, or three hundred and fifty-seven thousand billions of cubical miles. If the former number be divided by the latter, the quotient will be 68,428,800,000, showing that the nebula in question would contain within its circumference sixty-eight thousand, four hundred and twenty-eight millions, and eight hundred thousand globes as large as the SUN. A body of such a bulk is more than thirty-four billions, two hundred thousand millions of times larger than all the primary planets and their satellites which belong to our system. What is the special destination of such huge masses of matter, or what important designs they subserve in the physical and moral arrangements of the Governor of the universe, it is be yond our power, in the mean time, to form even a probable conjecture. Future generations may perhaps be enabled to throw some light on this subject, though it is probable that the nature, properties, and ultimate designs of many such objects will only be fully disclosed throughout the revolutions of that interminable duration which succeeds the short span of human existence; but of this we may rest assured, that they are not useless masses of materials in the universe, but are subservient to purposes worthy of Him whose wisdom is infinite and whose understanding is unsearchable. The four figures towards the right hand of the plate, marked No. 69, represent some specimens of planetary nebula. One of those bodies may be seen near the star v Aquarii, as above stated. Its right ascension is nearly 20h 52', and its south declination about 12° 26'. It lies north by west of the star Deneb Algedi, at the distance of about ten degrees. Other nebulæ of this description may be found near the following stars: 3 p Sagittæ, 14 Andromeda, 63 b Crateris, 61 g Sagittæ, 10 Camelopardus, 36 Ursa Majoris, 6 Navis, and 6 Draconis. About three minutes west from the star 16 c Cygni the following phenomenon is found: A bright point a little extended, like two points close to each other. It is as bright as a star of the eighth or ninth magnitude, surrounded by a very bright milky nebulosity, suddenly terminated, having the appearance of a planetary nebula with a lucid centre. The border is not well defined; it is perfectly round, and about one minute and thirty seconds in diameter. This is a beautiful phenomenon, and of a middle species between the planetary nebula and nebulous stars. Sir John Herschel, during his late residence at the Cape of Good Hope, is said to have discovered several new and singular objects in the southern hemisphere, some of them bearing a certain relation to the objects now described; among others, he is said to have detected a beautiful planetary nebula, which presents a perfectly sharp, well-defined disk of uniform brightness, exhibiting the exact appearance of a small pianet with a satellite near its margin. The regular compactness and globular form of such objects seem to indicate that they. are bodies sui generis, neither collections of distinct stars nor exactly of the same nature with the other masses of nebulous matter dispersed through the heavens. They seem to present a view of an immense system already completed, but of what 198 NEBULA IN ORION. nature it would be vain to conjecture. Another phenomenon of this kind is stated as being of an extraordinary nature, on account of the blue colour which its light exhibits. He has likewise discovered a close double star involved in the centre of a nebulous atmosphere, which is considered as a new and singular object. SECTION IV.-On the nebula in Orion. One of the largest and most remarkable nebulæ in the heavens is that which is found in the constellation of Orion. When a common observer looks at that constellation, the first object that arrests his attention is the three brilliant stars equidistant from each other in a straight line, which is called the belt of Orion. Immediately below these, hanging down, as it were, from the middle of the belt, three small stars at nearly equal distances are perceived, which are termed the sword. On directing the naked eye to the middle star of the three, the observer perceives something that has the appearance of a small star, but not well defined; this is the great nebula of Orion; of which, however, he can form no definite conception till his eye be assisted by optical instruments. With a common one-foot pocket achromatic telescope the nebulosity may be plainly perceived; but the higher the magnifying power, and the larger the aperture of the object glass, the more brilliant and distinct does this phenomenon appear, along with a number of small stars connected with it, which are quite invisible to the unassisted eye. The first who discovered this phenomenon was the celebrated Huygens, who gave the following description of it in his Systema Saturnium: "Astronomers place three stars close to each other in the sword of Orion; and when I viewed the middlemost with a telescope in the year 1656, there appeared, in the place of that one, twelve other stars; among these, three that almost touch each other, and four more besides appeared twinkling as through a cloud, so that the space about them seemed much brighter than the rest of the heavens, which appearing wholly blackish, by reason of the fair weather, was seen as through a certain opening, through which one had a free view into another region which was more enlightened. I have frequently observed the same appearance in the same place without any alteration; so that it is likely nomenon ature, on He has he centre new and æ in the of Orion. , the first tars equicalled the Own, as it at nearly he sword. he three, arance of nebula of onception h a com sity may e cele- ere ap- as more earance is likely |