A Treatise on Astronomy, Theoretical and Practical, Volumen1

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Smith, 1821 - 875 páginas
 

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Página 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.
Página 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.
Página 531 - 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
Página 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.
Página 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...
Página 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.
Página 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'.
Página 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...
Página 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.
Página 288 - ... in its situation. By the middle of April it appeared to be returning back again towards the north; and about the beginning of June, it passed at the same distance from the zenith as it had done in December, when it...

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