the naked eye; and Uranus, with a moderate magnifying power, appears about as bright as Saturn. How small a quantity of solar light may suffice for the purpose of vision will be obvious by attending to the following circumstance: In the late solar eclipse which happened on the 15th of May, 1836, little more than the one twelfth part of the sun was visi ble at those places where the eclipse was annular. Almost every person imagined that a dismal gloom and darkness would ensue, yet the diminution of light appeared no greater than what frequently happens in a cloudy day. At the time of the greatest obscuration there was more than half the light which falls upon Uranus, and all the objects of the surrounding landscape, though somewhat deficient in brilliancy, were distinctly perceived. There can be no doubt that the organs of vision of the inhabitants of the different planets, being formed by Divine wisdom, are exactly adapted to the objects amid which they are placed, and the quantity of light reflected from them; and there may be innumerable modes, unknown to us, by which this end may be effected. We can easily conceive, that if the pupils of our eyes were rendered capable of a greater degree of expansion than they now possess, or were the retina, on which the images of objects are depicted, endowed with a greater degree of nervous sensibility, so as to be more easily affected by the impulses of light, we might perceive as much splendour on all the objects connected with Uranus, were we placed on that planet, as we now do on the scenery around us during the brightest days of summer. When we pass from the light of the sun into a darksome apartment, on our first entrance we can scarcely distinguish any objects with distinctness; but after remaining five or six minutes, till the pupil has time to expand, every object around us is readily perceived; and, from the same cause, nocturnal animals can pursue their course with ease and certainty amid the deepest shades of night; so that the inhabitants of the most distant planet of our system, although it were removed from the sun to double the distance of Uranus, might perceive objects with all the distinctness requisite for the purposes of vision; and if the pupils of the eyes of such beings be much more expansive than ours (as is probably the case,) it is highly probable they will be enabled to penetrate much further into the celestial regions, and to perceive the objects in the firmament with much greater distinctness and space-penetrating power" than we can do, even with the aid of instruments. It is likewise probable that the objects on the surface of the more distant planets of our system are fitted to reflect the rays of light with peculiar brilliancy. Hence we find that the light of Uranus, though descending upon us from a region 900 millions of miles further than Sa turn, appears as vivid as the light which is reflected to us from that planet. The apparent diameter of the sun, as seen from Uranus. is only 1 minute, 38 seconds; whereas his mean apparent diameter as seen from the earth is 32 minutes, 3 seconds; consequently this orb, as viewed from this planet, will appear very little larger than Venus appears to us in her greatest brilliancy, or Jupiter when near his opposition. The following figure represents to the eye the apparent size of the sun as seen from Uranus and from the earth, the small circle representing his size as seen from Uranus. Fig. 66. Temperature of Uranus.-If heat followed the same law as the propagation of light, and decreased as the square of the distance of the planet from the sun increased, then the surface of the planet Uranus would be a cold region indeed, in which no life or animation, such as we see around us, could exist. Baron Fourier, in his "Memoir of Herschel," says, "Its temperature is more than forty degrees below that of ice;" and if the degrees of Reaumur's thermometer be meant, this temperature will correspond to one hundred and twenty-two degrees below the freezing point of Fahrenheit; a cold enough region, truly. In accordance with such representations, the poets of the last century expatiated on the cold temperature of Saturn in such strains as the following: "When the keen north with all its fury blows, Congeals the floods, and forms the fleecy snows, 'Tis heat intense to what can there be known; Warmer our poles than is its burning zone. Who there inhabit must have other powers, Juices, and veins, and sense, and life, than ours. One moment's cold, like theirs, would pierce the bone, Freeze the heart's blood, and turn us all to stone." BAKER'S Universe. This, it must be admitted, is a very cold poetic strain, almost sufficient to make one shiver, and to freeze our very thoughts; and if such a description were applicable to Sa turn, it is much more so to the planet Uranus, at double the distance. But I presume it is more in accordance with poetic license than with the deductions of sound philosophy. We have no valid reason to conclude that the degree of heat on the surfaces of the different planets is inversely proportional to the squares of their respective distances from the sun. The sun is to be considered chiefly as the great storehouse of light, and it may likewise be viewed as the great agent in the production of heat, without supposing it to be an enormous mass of fire, which the common opinion seems to take for granted. Its rays produce heat chiefly by exciting an insensible action between caloric and the particles of matter contained in bodies; and caloric appears to be a substance universally diffused throughout nature. If the degree of heat were in proportion to the distance from the sun, why should the upper regions of the atmosphere be so intensely cold? Why should the tops of lofty mountains be crowned with perpetual snows, while the plains below are scorched with heat? Why should an intense cold be felt in the latitude of 40°, when a comparative mildness is experienced in the latitude of 56°? In the state of Connecticut, North America, in January, 1835, the thermometer ranged from minus 25° to 27° of Fahrenheit; while in Scotland, during the same period, it was seldom so low as the freezing point. But as I have already thrown out some remarks on this subject when describing the planet Mercury, I need not enlarge (see page 34.) In order to form correct ideas of the distribution of heat among the planetary bodies, we have only to suppose that the Creator has proportioned the quantity of caloric (or that which produces sensible heat) to the distance at which every planet is placed from the sun, so that a large quantity exists in Saturn and a smaller quantity in Mercury. If, therefore, the quantity of caloric connected with Uranus be in proportion to its distance from the sun, there may be as much warmth experienced in that distant region of the solar system as in the mildest parts of our temperate zones. So that we are under no necessity of associating the frigid and gloomy ideas of the poet with our contemplations of this expansive globe. At all events, we may rest assured that the Creator, whose wisdom is infinite in its resources, and whose "tender mercies are over all his works," has adapted the structure and constitution of the inhabitants of every planet to the nature and circumstances of the habitation provided for them, so as to render every portion of his dominions a comfortable abode for his intelligent offspring; provided they do not frustrate his benevolent designs (as has been done in our world) by their rebellion and immoral conduct. For in no region of the universe, whatever may be its physical arrangements, can true happiness be enjoyed, unless love to God and love to all surrounding intelligences form the grand principles of action, and be uniformly displayed in every intercourse and association, and amid all the ramifications of moral conduct. On this basis chiefly rests the happiness of the intelligent universe; and, wherever principles directly opposite to these prevail among any order of intellectual beings, whatever may be the structure or scenery of their habitation, misery and moral disorder must be the inevitable consequence. The following additional particulars may be stated in relation to this planet: Its density is reckoned to be nearly equal to that of water. A body weighing one pound on the earth's surface would weigh only fourteen ounces, fourteen drachms, if removed to Uranus. The eccentricity of its orbit is 85,000,000 of miles, which is about the 1-42 part of its diameter. Its mean apparent diameter, as seen from the earth, is about four seconds. The inclination of its orbit to the ecliptic is forty-six minutes, twenty-six seconds, so that it is never much more than three-fourths of a degree from the ecliptic. This inclination is less than that of any of the other planetary orbits. Six satel lites are supposed to be connected with Uranus, but their periods and other phenomena have not yet been accurately ascertained. In the preceding pages I have given a brief sketch of the principal phenomena connected with the primary planets of our system. Whether any other planets besides those specified belong to this system is at present unknown. We have no reason to believe that the boundaries of the planetary system are circumscribed within the range of our discoveries or the limits of our vision. Within the space of little more than half a century, the limits of this system have been expanded to our view to double the extent which they were formerly supposed to comprehend. Instead of an area of only 25,400,000,000 of square miles, it is now found to comprise an extent of 101,700,000,000 of square miles, which is four times the dimensions formerly assigned to it. There would be no improbability in conceiving it extended to at least triple these dimensions. Within the space of twenty-six years, from 1781 to 1807, no fewer than five primary planets and eight secondaries were discovered, besides a far greater number of comets than had ever before been detected within a similar lapse of years; and therefore it would be obviously rash and premature to conclude that we have now discovered all the moving bodies of our system. Far beyond the limits of even Uranus other planets yet unknown may be performing their more ample circuits around the sun; for we know, from the case of comets, that even throughout those distant regions his attractive power and influence extend. In the immense interval of 900,000,000 of miles between the orbits of Saturn and Uranus, one, if not two planets may possibly exist, though they have hitherto eluded the observation of astronomers. In order to detect such bodies, if any exist, it would be requisite to survey, more minutely than has yet been done, a zone of the heavens extending at least twenty degrees on each side of the ecliptic, marking exactly the minutest objects in every part of it which the most powerful telescopes can enable us to descry. After which a second survey should be made to ascertain if any of the bodies formerly observed be found amissing or have shifted their position. It might likewise be expedient to compare with new observations the stars marked in all the celestial atlases that have hitherto been published, and to note particularly those which are wanting where they were formerly marked, and those that have appeared in certain places where they were formerly unobserved. If a taste for celestial investigations were more common among mankind, and were the number of observers indefinitely increased, there would be no great difficulty in accomplishing such an object; for certain small portions of the heavens might be allotted to different classes of observers, who might proceed simultaneously in their researches, and in a comparatively short period the whole survey might be completed. It is not improbable that a planet may exist within the space of 37 millions of miles which intervenes between the orbit of Mercury and the sun. But such a body could never be detected in the evening after sunset, as its greatest elongation from the sun could not be supposed to be more than ten or twelve degrees, and, consequently, it would descend below the horizon in about half an hour after sunset, and before twilight had disappeared. The only chance of detecting such a planet would be when it happened to transit the sun's disk; but as this would happen only at distant intervals, and as it might make the transit in cloudy weather, or when the sun is absent from our hemisphere, there is little prospect of our discovering such a body in this way. It might be of some importance, however, that those who make frequent observations on the sun should direct their attention to this circumstance; as there have been some instances in which dark bodies have been observed to move across the sun's disk in the space of five or six hours, when no other spots were visible. An opaque body of this description was seen by Mr. Lloft and others on the 6th of January, 1818, which moved with greater rapidity across the solar disk than Venus in her transit in 1769. It is possible that a planet within the orbit of Mercury might be detected in the daytime, were powerful telescopes applied to a space of the heavens about ten or twelve degrees around the sun. Small stars have been seen even at noonday with powerful instruments, and, consequently, a planet even smaller than Mercury might be perceived in the daytime. In this case, a round opaque body would require to be placed at a considerable distance from the observer, so as completely to intercept the body of the sun, and about a degree of the heavens all around him; and every portion of the surrounding space, extending to at least twelve degrees in every direction, should then be carefully and frequently examined. Such observations, if persevered in, would undoubtedly afford a chance of detect ing any revolving body that might exist within such a limit. But I may afterward have an opportunity of describing more particularly the observations, and the mode of conducting them, to which I allude. X. THE SUN. Having taken a cursory survey of the most prominent particulars connected with the primary planets, I shall now proceed to a brief description of the sun, that magnificent luminary on which they all depend, from which they derive light, and heat, and vivifying influence, and by whose attractive energy they are directed in their motions and retained in their orbits. Before proceeding to a description of the particular phenomena connected with the sun, it may be expedient briefly to describe some of his apparent mo tions. Apparent Motions of the Sun.-The most obvious apparent motion of the sun, which in known to every one, is, that he appears te rise in the morning in an easterly direction to traverse a certain portion of the sky, and then to disappear in the evening in a direction towards the west. Were we to commence our observations on the 21st of December, in the latitude of 52° north, which nearly corre sponds to that of London, we should see the sun rising near the southeast point of the horizon, as at S E, Fig. 67, describing a com paratively small curve above the horizon, from SE to S W, in the southern quarter of the heavens, and setting at S W, near the southwest. At this season the sun remains only between seven and eight hours above the horizon; and when he arrives at S, at midday, which is the highest point of his elevation, he is only about fourteen degrees above the horiFig. 67. zon, which may be represented by the line S B. After disappearing in our horizon in the evening, he describes the large curve from S W to W, N, and E, till he again arrives in the morning near the point S E. All this curve is described below our horizon, and, therefore, the nights at this season are much longer than the days. After this period the sun rises every day at points a little further to the north, between SE and E, and sets in corresponding points in the west, between S W and W, till the 21st of March, when he rises at the point E, due east, and sets due west at the point W. At this time he moves through the semicircle E, S, W, and at noon he rises to the elevation of thirty-eight degrees above the southern horizon, which may be represented by the line S C. This is the period of the vernal equinox, when there is equal day and night throughout every part of the earth, the sun being twelve hours above and twelve hours below the horizon. After this period the sun rises to the north of the easterly point, and sets to the north of the westerly, and the length of the day rapidly advances till the 21st of June, when he rises near the north-east point, N E, and sets near the north-west point, N W, describing the large curve from NE to ES W, and N W. This period of the year is called the summer solstice, when the days are longest, at which time the sun rises at noon to an elevation of 614 degrees above the horizon, which may be represented by the line S D, and he continues above the horizon for nearly seventeen hours. The length of the nights at this time is exactly the same as the length of the days on the 21st of December. The sun's nocturnal arch, or the curve he describes below the horizon, is that which is represented in the lower part of the figure from N W to N E. In more southern latitudes than fifty-two degrees, the sun rises to a higher elevation at noon; and in higher latitudes his meridian altitude is less than what is stated above. From the time of the summer solstice the days gradually shorten; the sun rises in a more southerly direction till the 23d of September, which is called the autumnal equinox, when he again rises in the eastern point of the compass, and every succeeding day at a point still further to the south, till, on the 21st of December, or the winter solstice, he is again seen to rise near the south-east, and afterward to pass through all the apparent variations of motion above described. Were we residing in southern latitudes, such as those of Buenos Ayres, the Cape of Good Hope, or Van Diemen's Land, the apparent motions of the sun would be somewhat different. Instead of beholding the sun moving along the southern part of the sky from the left hand to the right, we should see him direct his course along the northern part of the heavens from the right hand to the left. In other respects his apparent motions would nearly correspond to those above described. Were we placed in countries under the equator at the time of the equinoxes, the sun at midday would shine directly from the zenith, at which time objects would have no shadows. At all other times the sun is either in the northern or the southern quarter of the heavens. During the one half of the year he shines from the north, and the shadows of objects fall to the south; during the other half he shines from the south, and the shadows of all objects are projected towards the north. This is a circumstance which can never occur in our climate or in any part of the temperate zones. At the equator, too, the days and nights are of the same length, twelve hours each, throughout the whole year. Were we placed at the poles, the motion of the sun would present a different aspect from any of those we have described. At the north pole, on the 21st of March, we should see a portion of the sun's disk appear in the horizon after a long night of six months. This portion of the sun would appear to move quite round the horizon every twenty-four hours; it would gradually rise higher and higher till the whole body of the sun made its appearance. As the season advanced, the sun would appear to rise higher and higher till he attained the altitude of 234 degrees above the horizon, which would take place on the 21st of June; after which his altitude would gradually decline till the 23d of September, when he would again appear in the horizon. During the whole of this period of six months there is perpetual day, he stars are never seen, and the sun appears to go quite round the heavens every twenty-four hours without setting, in circles nearly parallel to the horizon. After the 23d of September the sun disappears, and a night of six months succeeds, which is occasionally enlivened by the moon, the stars, and the corruscations of the aurora borealis, during which period the south pole enjoys all the splendour of an uninterrupted day. In all places within the polar circles, the length of the longest day varies from twenty-four hours to six months. In the northern parts of Lapland, for example, the longest day is about six weeks; during this time the sun appears to move round the heavens without setting; but at noon, when he comes to the meridian, he is about 40 degrees above the southern horizon, and twelve hours afterward he appears elevated about six degrees above the northern horizon, from which point he again ascends till he arrives at the southern meridian. Such are the apparent diurnal motions and general aspects of the sun in different parts of the earth, which are owing partly to the inclination of the axis of the earth to the plane of the ecliptic, and partly to the different positions in which a spectator is placed in different zones of the globe. It is almost needless to remark, that these motions of the sun are not real, but only apparent. While presenting all these varieties of motion, he is still a quiescent body in the centre of the planetary system. By the rotation of the earth round its axis, from west to east, every twentyfour hours, all these apparent motions of the sun are produced. This we have already endeavoured to prove in chap. i. p. 17-19. Besides the apparent diurnal motion now described, there is another apparent motion of the sun in a contrary direction, which is not so much observed, and that is, his apparent motion from west to east through the whole circle of the heavens, which he accomplishes in the course of a year. This motion manifests itself by the appearance of the heavens during the night. The stars which lie near the path of the sun, and which set a little time after him, are soon lost in his light, and after a short time reappear in the east a little before his rising. This proves that the sun advances towards them in a direction contrary to his diurnal motion; and hence we behold a different set of stars in our nocturnal sky in summer and in winter. This apparent revolution of the sun is produced by the annual motion of the earth round the sun, of which I have already given an explanation (chap. i. p. 19,) along with certain demonstrative proofs that the sun is the centre of the planetary system, (see also chap. ii. p. 26-31.) Distance and Magnitude of the Sun.-To find the exact distance of the sun from the earth is an object which has much interested and engaged astronomers for a century past. The angle of parallax being so small as about eight and a half seconds, rendered it for some time difficult to arrive at an accurate determination on this point, till the transits of Venus in 1761 and 1769. From the calculations founded upon the observations made on these transits, it has been deduced that the distance of the sun is about 95,000,000 of miles. This distance is considered by La Place and other astronomers to be within the 1-87 part of the true distance, so that it cannot be much below 94 millions on the one hand, nor much above 96 millions on the other. Small as this interval may appear when compared with the vast distances of some of the other celestial bodies, it is, in reality, a most amazing distance when compared with the spaces which intervene between terrestial objects; a distance which the mind cannot appreciate without a laborious effort. It is thirty-one thousand six hundred times the space which intervenes between Britain and America; and were a carriage to move along this apace at the rate of 480 miles every day, it would require 542 years before the journey could be accomplished. The magnitude of this vast luminary is an object which overpowers the imagination. Its diameter is 880,000 miles; its circumference, 2,764,600 miles; its surface contains 2,432, 800,000,000 of square miles, which is twelve thousand three hundred and fifty-times the area of the terraqueous globe, and nearly fifty thousand times the extent of all the habitable parts of the earth. Its solid contents comprehend 356,818,739,200,000,000, or more than three hundred and fifty-six thousand billions of cubical miles. Were its centre placed over the earth, it would fill the whole orbit of the moon, and reach 200,000 miles beyond it on every hand. Were a person to travel along the surface of the sun, so as to pass along every square mile on its surface, at the rate of thirty miles every day, it would require more than two hundred and twenty millions of years before the survey of this vast globe could be completed. It would contain within its circumference more than thirteen hundred thousand globes as large as the earth, and a thousand globes of the size of Jupiter, which is the largest planet of the system. It is more than five hundred times larger than all the planets, satellites, and comets belonging to our system, vast and extensive as some of them are. Although its density is *In some editions of the" Christian Philosopher," under the article Astronomy, this number is two thousand millions, should be two hundred mil inaccurately stated; and the number which follows, livre. |