## Popular Astronomy: A Series of Lectures Delivered at Ipswich |

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aberration of light accurate angle angular distance appear ascertain astronomers ball body bright star calculation Cape Cavendish experiment celestial clock computed curve described diameter direction disturbed earth earth's axis earth's centre earth's equator ecliptic effect ellipse equatoreal exactly explain Figure 43 fluid globe Greenwich heavens horizon hour inclination Jupiter lecture length lunar precession Mars mean density method millions of miles moon mountain move Mural Circle nearly North Pole nutation object observations Observatory orbit parallax passes the meridian path pendulum perpendicular perturbations planets plumb-line point of Aries Polar Star position precession produced proportion pull refraction remark revolve rotation round the sun satellites seen sidereal day solar South Pole spheroid square sun's attraction sun's distance suppose supposition surface tance telescope theory of gravitation thing tion transit instrument transit of Venus triangle velocity vertical vibrations whole yard measure Zenith Sector

### Popular passages

Page 229 - But if it is true that every particle of matter attracts every other particle of matter, with a force varying inversely as the square of the distance...

Page 273 - EG ; and then, as in the last method, the proportion of EG to GM is the same as the proportion of the mass of the moon to the mass of the earth.

Page 196 - ... In the southern hemisphere, there is the bright star of the Centaur, (Alpha Centauri,) for which it would seem that the inclination of the two lines from the opposite sides of the earth's orbit to the star, is an angle of two seconds and no more. An angle of two seconds is that in which a circle f5 of an inch in diameter would be seen at the distance of a mile.

Page 126 - ... the squares of the times of revolution of the different planets are in the same proportion as the cubes of their mean distances from the sun.

Page 287 - ... we can immediately infer the other. Now, pendulum observations afford us the means of determining the force of gravity at any place, (page 248,) and therefore, if the times of vibration of a pendulum at the top and bottom of a mine be found, the ratio of the force of gravity at the top to that at the bottom may be calculated, and thence the ratio of the mean density of the earth to that of its surface. This mode of determining the mean density was put in practice by the Astronomer Royal, at the...

Page 286 - Electricity is usually developed, in order to show its effects, by the friction of glass. The earlier electricians, in the prosecution of their researches, merely used glass tubes or other nonconductors, held in one hand and...

Page 187 - Now the sun attracts the moon, and disturbs it as he would the path of the mountain we have just supposed, and the effect is the same — viz., the intersections of the moon's orbit with the ecliptic travel backward, completing a revolution in about 18 years. During half of this time the moon's orbit is inclined to the ecliptic in the same way as the earth's equator ; during the other half it is inclined in the opposite way. In the former state, the moon's attractive tendency to tilt the earth is...

Page 102 - Kepler made out was this : that the orbits of planets are ellipses. Another important thing made out was this: that the planets describing these ellipses move with very different velocities at different times. Each planet, when in that part of its orbit which is nearest to the sun, travels quickly, and when in that part which is furthest from the sun, travels slowly. The way in which he expressed the law of motion is this : if in one part of the orbit I draw two lines SK, SL, from the sun, inclosing...

Page 181 - ... it descend to cut the plane of the ecliptic sooner than it otherwise would, and therefore, in both halves of the diurnal rotation (as at the winter solstice) the place of intersection of the earth's equator with the ecliptic will move in the direction opposite to the earth's rotation. At the equinoxes, the plane of the earth's equator passes through the sun, and then the sun's action does not tend to tilt the earth at all, and consequently does not tend to alter the position of its equator at...

Page 132 - This rule is expressed in mathematical terms, by saying that the squares of the periodic times are in the same proportion as the cubes of the distances ; and was of great importance to Newton in leading him to the law of the sun's attractive force.