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Rh of the inclination and node of the apparent path of the comet with regard to the ecliptic, which Tycho found from two latitudes and the arc of the ecliptic between them; seven different combinations give results which only differ a few minutes inter se. The sixth chapter is a more lengthy one, and treats of the distance of the comet from the earth; and as this was of paramount importance as a test of the Aristotelean doctrine, he endeavours to determine the parallax in several different ways. First, he shows that the comet had moved in a great circle, and though not with a uniform velocity throughout, yet with a very gradually decreasing one; and if it had been a mere "meteor" in our atmosphere, it would have moved by fits and starts, and not in a great circle. The velocity never reached half that of the moon, the nearest celestial body. He next discusses two distance measures from Pegasi, made on the 23rd November, with an interval of three hours, and finds that if the comet had been at the same distance from the earth as the moon, the parallax would have had the effect of making the second angular distance from the star equal to the first, even after allowing for the motion of the comet in the interval, while the second observed distance was 12′ smaller than the first one. At least the comet must have been at a distance six times as great as that of the moon, and all that can be concluded from the distance measures is that the comet was far beyond the moon, and at such a distance that its parallax could not be determined accurately. The same appears from comparisons between distance measures from stars made at Hveen and those made at Prague by Hagecius, which should differ six or seven minutes if the comet was as near as the moon, whereas they only differed one or two minutes. The observations of Cornelius Gemma at Lou vain, when compared with those at Hveen, point in the same direction, but are much