the north by Andromeda; east by Aries and Triangulum; south by Cetus; and west by Aquarius and Pegasus. TELESCOPIC OBJECTS The brightest star in Pisces is a of the third magnitude, it is a double star, both of which it is composed are white. is a very beautiful double star. 35 and 38 are double stars of a pale red colour. L, K, 4, 35, 51, 76, 77, and 100, are double stars. A faint nebula near The star numbered 108 is missing. COMETARY ASTRONOMY. ON THE PROBABILITY OF A CONCUSSION OF A COMET WITH THE EARTH. It has been stated that the comet of 1770 passed through the system of the planet Jupiter, without in the slightest degree affecting the motions of either the primary or his satellites; also, that it passed sufficiently near our planet to have shortened the length of the year had its mass been equal to that of the earth. No effect whatever was produced, from whence it may be concluded, that the neighbourhood of a comet is not of sufficient importance to excite any alarming apprehensions for the safety of the habitation of man. Most of the calculations that have been made respecting the effect of the proximity of a comet to our earth have proceeded on erroneous principles,-over-rating the quantity of matter in comets, and losing sight of their great velocity when in this part of the system. For a comet to produce any direful effect, it ought to contain not merely a considerable quantity of matter, but also ought to be vertical and stationary to the earth's surface for several hours; instead of which, we have sufficient reason to believe that though vast in volume, comets contain but little matter in proportion, consequently, their attractive energy would be inconsiderable; also their velocity would, in a very short period, carry them beyond the limit of exerting any influence on the waters of the globe. Of course, this general statement would be modified by the rate and direction of a comet's motion, and also the earth's rotation. It may, then, be asserted with safety that the close appulse of a comet would not be attended with any fatal results; and that this security principally consists in its great velocity, which would so swiftly remove it to a distance. But, the very circumstance which, in the case of proximity, would be the security of our globe, (its velocity,) would, in the event of a contact, be attended with the direst effects. It is true that the probability of a contact is less, in an almost infinite degree, than the proximity of a comet, which, notwithstanding, is an event which every astronomer is fully aware, is within the verge of possibility. The effects of a contact would be greatly modified by circumstances. Should the comet strike the earth obliquely, it would glance off, and the consequences would be partial. If the point of collision were on a continent of the globe, mountains would be hurled from their bases, and new ones would elevate their ridges towards the clouds. Were the place of meeting on either of the great oceans, some regions would be deserted, and others would be inundated by the waters of the sea. These dreadful consequences would be increased, in an inde finite proportion, if the point of contact were in the direction of the earth's centre; the meeting would be terrific; the earth's period of revolution would, in all probability, be altered, either by carrying it nearer to or farther from the sun; a different inclination of the axis might be given, and there would be a consequent change of seasons; the diurnal motion might be either accelerated or retarded, by which the length of the day would be affected; the vast continents of the globe would be again covered with the ocean, which, deserting its bed, would rush towards the new equator! Infinitely more tremendous would be the catastrophe if the earth were struck by a retrograde comet in the direction of the terrestrial centre, the comet making up, by its velocity, the deficiency of mass in this case the centrifugal force of both bodies might be annihilated,— the centripetal principle alone obeyed, and both comet and earth rush to the sun! It must, however, be stated, that the probability of such an event is all but infinitely removed: the most likely of any that is known, to effect such a consummation, is the comet of Encke, which it has been calculated would come in collision with our earth after a lapse of 219 millions of years! This calculation proceeds on the soundest principles of reasoning, and proves not so much the safety of our globe from cometary destruction, (for some comet, hitherto unseen by mortal eyes, may now be winging its flight directly towards our globe,) as the astonishing powers of the mind of man, which can thus essay to penetrate the veil of futurity, and read the destiny of a world. But destruction to this terrestrial orb and its teeming inhabitants, may be more speedily brought about than by a concussion with these celestial agents. A single principle of motion annihilated, evaporation suspended, or a component part of the atmosphere abstracted, and "final ruin would drive her ploughshare o'er creation;" universal conflagration would instantly ensue from the separation of the oxygen from the nitrogen of the atmosphere, the former exerting its native energies without control wherever it extends,-solid rocks, ponderous marble, metals, and even water itself, would burst into an intensity of flame, and change the aspect of all sublunary things. But all these vast bodies of the universe are, doubtless, kept in their prescribed limits as with so many "reins and bridles," and when this earth has completed its destined circles, and fulfilled the purposes for which it was called out of nothing, it will need but the command of the glorious Creator who at first spoke this beautiful frame into being, bliss, and light, to return it to its primeval gloom, or bid it shine forth with new resplendent beauty and lustre. |