Verwandte Artikel zu Library of useful knowledge Volume 3; Natural philosophy
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Inhaltsangabe
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1834 Excerpt: ...of the summer solstice, with one made 145 years previously by Aristarchus of Samos, discovered this to be too great. He found that the solstice arrived 12 hours sooner at the end of these 145 years than it ought to have done, on the supposition of the solar year being 365J days; 12 hoursdivided by 145 gave him the diminution to be made on the length of the year. In this way he found for the length of the tropical year 365 days 5 hours 55 minutes 12 seconds. The sun appearing to move in a circle round the earth, it was natural to suppose that his motion in the ecliptic was uniform; andj such was probably the « V. Delambre, Astron. Anc. YoL I. p. 142. opinion of the early astronomers of Greece. However when they began to make observations with the gnomon, they could not help perceiving a considerable difference between the intervals of the equinoxes and solstices; intervals which must be equal were the motion of the sun round the earth uniform. Hipparchus undertook to investigate this point. He observed that the interval between the vernal equinox and the summer solstice was 94J days; between the summer solstice and the autumnal equinox 924 Thus the sun took 187 days to describe the northern half of the ecliptic, and only 178 for the southern half; indicating a considerable increase of velocity during the latter. To explain this irregularity, Hipparchus supposed the sun to move round the earth m an exeentric circle; that is in a circle, whose centre did not coincide with that of the earth. It is clear, that in this case the sun, though moving uniformly in its orbit, would appear to a spectator at the earth to move with an unequal velocity, on account of the variation of its distance. The question Was to determine the quantity of this excentricity, that i...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1834 Excerpt: ...of the summer solstice, with one made 145 years previously by Aristarchus of Samos, discovered this to be too great. He found that the solstice arrived 12 hours sooner at the end of these 145 years than it ought to have done, on the supposition of the solar year being 365J days; 12 hoursdivided by 145 gave him the diminution to be made on the length of the year. In this way he found for the length of the tropical year 365 days 5 hours 55 minutes 12 seconds. The sun appearing to move in a circle round the earth, it was natural to suppose that his motion in the ecliptic was uniform; andj such was probably the « V. Delambre, Astron. Anc. YoL I. p. 142. opinion of the early astronomers of Greece. However when they began to make observations with the gnomon, they could not help perceiving a considerable difference between the intervals of the equinoxes and solstices; intervals which must be equal were the motion of the sun round the earth uniform. Hipparchus undertook to investigate this point. He observed that the interval between the vernal equinox and the summer solstice was 94J days; between the summer solstice and the autumnal equinox 924 Thus the sun took 187 days to describe the northern half of the ecliptic, and only 178 for the southern half; indicating a considerable increase of velocity during the latter. To explain this irregularity, Hipparchus supposed the sun to move round the earth m an exeentric circle; that is in a circle, whose centre did not coincide with that of the earth. It is clear, that in this case the sun, though moving uniformly in its orbit, would appear to a spectator at the earth to move with an unequal velocity, on account of the variation of its distance. The question Was to determine the quantity of this excentricity, that i...
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