Dr. Herschel then solves a general problem for computing the length of the visual ray; that of the telescope which he uses will reach stars 497 times the distance of Sirius. Now Sirius cannot be nearer than a hundred thousand times the length of the earth's orbit; therefore Dr. Herschel's telescope will at least reach 100,000 × 190,000,000 × 497 miles; and he says, that, in the most crowded part of the milky way, he has had fields of view that contained no less than 588 stars, and these were continued for many minutes, so that, in a quarter of an hour, he has seen 116,000 stars pass through the field of view of a telescope of only 15' aperture: and at another time, in 41 minutes, he saw 258,000 stars pass through the field of his telescope. Every improvement in his telescopes has discovered stars not seen before; so that there appears no bounds to their number, nor to the extent of the universe. In this month, the Sun rises to its highest part of the heavens on the 22d, but to casual observers its apparent meridian height will be the same for several days before and after the 22d. The times of the Sun's rising and setting will be as follow: Wednesday 1st, Sun rises 53 m. after 3. Sun sets 7 m. after 8 Saturday 11th Wednesday 22d The Sun will enter Cancer at 10 minutes after 3 in the morning on the 22d. On the 1st, Venus will pass over the star marked o X, the star being 38, north of the planet's centre: and on the 16th, Jupiter will eclipse the star, the star being one degree south of the planet's centre. Equation of Time. [See Explanation in January.] The following table will show what is to be subtracted from, and added to the apparent time, as exhibited by the dial, in order to set the clock or watch to equal or true time, for each 5th day of the month. m. s. Wednesday 1st, from the time shown by the dial SUBTRACT 2 40 The full Moon occurs at 15 minutes past I in the morning of the 3d day: it enters its last quarter at 27 minutes past 4 in the morning of the 11th. The change or new Mcon is 32 minutes: past 11 at night on the 17th, and it will enter its first quarter at 33 minutes past 4 in the afternoon of the 24th. The time of the Moon's rising on the first four days after she is full will be as follows, viz. June 4th, 30 min. past 9 in the evening, 5th, 21 ditto. 11 ditto. 11 ditto. The superior conjunction of Mercury will be at 12 at noon on the 6th of June. There will be but one eclipse of Jupiter's first satellite visible, of which the emersion will take place at 40 minutes past 10 in the evening of the 15th. On the 17th, at 50 minutes past 10 o'clock at night, there will be an eclipse of the second satellite. This will be the time of the emersion also; therefore, to see this and the other eclipse, the observer must be at his stand a proper time previously. VIEW OF THE SOLAR SYSTEM. Of the Earth. Although we have spoken of the motions of the earth as certain, yet it may be worth while to enter a little more at large on the subject. The motion of the earth,' says a good writer, has so long ceased to be a disputed question, that the arguments on each side are nearly forgotten; and those who do not scruple to adopt the hypothesis of the earth's mo tions, are often less acquainted with the arguments on which it is supported, than they would have been in former times, when their opinions must have been the subjects of fierce contention,' Of the modern writers on this topic, La Place seems to have collected these arguments together in the most popular and perspicuous form. Of these we shall give a cursory account. When we reflect on the diurnal mo- tion to which all the heavenly bodies are subject, we recognize the existence of a general cause which moves them, or which seems to move them, round the axis of the earth. If we consider that these bodies are insulated, with respect to each other, and placed at very different distances from the earth; that the Sun and the stars are at a much greater distance from it than the Moon; and that the variations in the apparent diameters of the planets indicate great alterations in their distances; and, moreover, that the comets traverse the heavens freely, and in almost all directions, it will be difficult to conceive that it is the same cause which impresses on all these bodies a common motion of rotation. But since the heavenly bodies present the same appearances to us, whether the firmament carries them round theearth, considered as immoveable, or whether the earth itself revolves in a contrary direction, it seems much more natural to admit this latter motion, and to regard that of the heavens as only apparent. The earth is a globe, not 8000 miles in diameter; but the diameter of the Sun is nearly 100 times larger. If its centre coincided with that of the earth, its vo lume would not only embrace the orbit of the Moon, but extend much more than as far again; from hence we may judge of its immense magnitude: besides, its distance from the earth is 95,000,000 of miles. Is it not, then, more natural to attribute to the globe that we inhabit a rotatory motion on its own axis, than to suppose in a mass so enormous, and so remote from us as the Sun is, such an extremely rapid mo tion as would be requisite to revolve in one day round the earth? Let us consider, also, what an immense power it would require to contain it, and to counteract its centrifugal force; that is, to retain it in its orbit. Every one of the stars presents to us similar difficulties, which are all removed by admitting the revolution of the earth on its supposed axis. We have already observed, that the pole of the equator seems to move slowly round that of the ecliptic, from whence results the precession of the equinoxes. If the earth is immoveable, the pole of the equator is equally so, since it always corresponds to the same point of the terrestrial surface: the ecliptic, therefore, moves round these poles, and in this motion carries all the heavenly bodies with it. Thus, the whole system, composed of so many heavenly bodies, differing from each other in their magnitudes, motions, and distances, would be again subject to a general motion, which disappears, and is reduced to a very simple law, if we suppose the terrestrial axis to move round the poles of the ecliptic. According to the true theory, we are but in a similar situation, on a large scale, of a spectator placed in a ship that is in motion: we are carried on, it is true, with an immense velocity; which velocity is, however, common to every thing that surrounds us. The person on ship-board fancies himself at rest, and, the shore, the hills, and all the objects placed out of the vessel, appear to him to move. But on comparing the extent of the shore, and the heights, perhaps, of surrounding hills or mountains, he begins to suspect that the apparent motion of these objects arises from the real motion of himself. The stars which fill, as it were, the celestial regions, are, relatively to the earth, what the shores and hills are to the vessel; and the same reasons which convince the navigator of the reality of his own motion, prove, or ought to prove, to us the motion of the earth. It may be further observed, that in all the works of nature with which we are acquainted, the Creator appears to act by the shortest, easiest, and simplest means. Now if the earth be at rest, and the stars to move, the velocity of these latter must be immense; and yet all the purposes thereof might have been answered by a moderate motion of the earth alone. The Moon's distance from the earth is 240,000 miles; of course, the length of the tract which it traverses, if it moves round the earth in 24 hours, is about 1,500,000; that is, at the rate of 62,500 miles in an hour, instead of 2290 miles, which is really the case; consequently, in each second of time, the Moon, known to be the slowest of all the heavenly bodies, must move more than 17 miles. Again, the Sun's mean distance from the earth is about 95,000,000 miles; consequently the diurnal path of that luminary, if it revolve about our globe in 24 hours, must be 580,000,000; and, therefore, in a single second, the beat of a watch, he must move nearly 7,000 miles. Upon the same principle, that is, supposing the earth to be the centre of the system, and not the Sun, the planet Mars, in a second of time, must travel at the rate of more than 10,000 miles, Jupiter 36,000, and Saturn 62,000. And, lastly, the fixed stars being yet indefinitely more remote from the earth than the Sun or Saturn, their motion in or near the equator must be vastly swifter than this. These arguments, and our author mentions many others, which are equally conclusive to the mathematician, though not so obvious to the general reader, are strengthened by analogy. A rotatory motion has been observed in several planets, and always from west to east, which is similar to that which the diurnal motion of the heavens seems to indicate in the earth. Jupiter, which is above a thousand times larger than the earth, moves, unquestionably, on its axis in less than 12 hours. An observer, on its surface, would see the heavens revolve round him in that time; yet we, as mere observers, know, in the case R |