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A Treatise on Astronomy: Theoretical and Practical: Part I-[Ii], Vol. 1 Volume 1
No preview available - 2015
aberration according altitude angle annual apparent Astronomical axis body called catalogue cause centre circle clock computed consequently correction corresponding declination deduced described determined difference direction Draconis Earth ecliptic effect epoch equal equation error exactly EXAMPLE explained expression Figure fixed former formula given greater greatest Greenwich half happen Hence horizon increase inequality instance interval known latitude latter least less longitude lunar mean measure meridian method minutes Moon Moon's motion move nearly node north polar distance nutation obliquity observations obtained orbit parallax passing period planet pole position preceding precession present quadrant quantity radius reason reduced refraction represent respectively right ascension round seen sidereal solar spectator star star's Sun's supposed Tables telescope term theory tion transit true variation Venus wire zenith distance
Page xix - Observer' at a salary of 100£ per annum, his duty being 'forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting the art of navigation.
Page 291 - ... south when it came about six in the morning. " Though I have since discovered that the maxima in most of these stars do not happen exactly when they come to my instrument at those hours, yet not being able at that time to prove the contrary, and supposing that they did, I endeavoured to find out what proportion the greatest alterations of declination in different stars bore to each other ; it being very evident that they did not all change their declinations equally.
Page 529 - The Equation of Time is computed by taking the Difference of the Sun's true right Ascension and his mean Longitude corrected by the Equation of the Equinoxes in right Ascension, and turning it into Time at the Rate of 1
Page 34 - M', M", &c. and E may, for small portions near those points, be held as parallel. Nn is the line of the nodes, that is, the intersection of the plane of the Moon's orbit with the plane of the ecliptic, or the plane of the Earth's orbit round the Sun.
Page 13 - ... accurately, to their own thinking, as we can to ours, in addition to which they have the evidences of their senses, which we have not, and Scriptures and facts in their favor, which we have not, it is not without some show of reason that they maintain the superiority of their system. Whereas, we must be content, at present, to take for granted the truth of the hypothesis of the earth's motion for one thing. We shall never, indeed, arrive at a time when we shall be able to pronounce it absolutely...
Page 71 - Y's. The Y's are placed in two dove-tailed brass grooves fastened in two stone pillars E and W, so erected as to be perfectly steady. One of the grooves is horizontal, the other vertical, so that, by means of screws, one end of the axis may be pushed a little forwards or backwards, and the other end may be either slightly depressed or elevated : which two small movements are necessary, as it will be soon explained, for two adjustments of the telescope.
Page 54 - In this case so that these instruments can be read off by the aid of their verniers to an accuracy of 10 seconds. The verniers occupy on the limbs spaces equal to 9° 50'.
Page 70 - AD is a telescope, fixed, as it is represented in the figure, to a horizontal axis formed of two cones.- The two small ends of these cones are ground into two perfectly equal cylinders ; which cylindrical ends are called Pivots. These pivots rest on two angular bearings, in form like the upper part of a Y, and denominated Y's. The Y's are placed in two dove-tailed brass grooves fastened in two stone pillars E and W, so erected as to be perfectly steady. One of the grooves is horizontal, the other...
Page 319 - I am of opinion, that if it were 1" I should have perceived it, in the great number of observations that I made, especially of y Draconis; which agreeing with the hypothesis (without allowing any thing for parallax) nearly as well when the sun was in conjunction with, as in opposition to, this star, it seems very probable that the parallax of it is not so great as one single second; and consequently that it is above 400,000 times farther from us than the sun.