# A Treatise on Astronomy

Harper, 1870 - Astronomy - 336 pages

### Popular passages

Page 126 - RULES TO KNOW WHEN THE MOVEABLE FEASTS AND HOLYDAYS BEGIN. EASTER DAY, on which the rest depend, is always the First Sunday after the Full Moon which happens upon, or next after the Twenty-first Day of March ; and if the Full Moon happens upon a Sunday, Easter Day is the Sunday after.
Page 264 - For, by the first of Kepler's laws, the areas described by the radius vector are proportional to the times, and when this is the case, by Art.
Page 285 - The names of the signs of the zodiac are: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces.
Page 48 - G, which carries the whole of the upper works, and also a pointer, to show the degree and nearest five minutes to be read off on the azimuth circle ; the remaining minutes and seconds being obtained by means of the two reading microscopes, C and D. The pillars HH support the transit axis, I, by means of the projecting pieces, LL. The telescope, MM, is connected with the horizontal axis in a manner similar to that of the transit instrument.
Page 20 - If the hands of the sidereal clock be set to Oh. Om. Os. when the first point of Aries is on the meridian, the clock (if it neither gains nor loses time) will afterward indicate at each instant the right ascension of any object which is then on the meridian, for the motion of the hands of the clock corresponds exactly with the apparent diurnal motion of the heavens. While 15° of the equator pass the meridian, the hands of the clock move through one hour.
Page 137 - ... at last brought down to the ground; and the greater the velocity is with which it is projected, the farther it goes before it falls to the earth. We may therefore suppose the velocity to be so increased, that it would describe an arc of 1, 2, 5, 10, 100, 1000 miles before it arrived at the earth, till at last, exceeding the limits of the earth, it should pass into space without touching it.
Page 66 - A solar day is the interval between two successive returns of the sun to the same meridian. The sun moves through 360 degrees of longitude in one tropical year, or 365 days, 5 hours, 48 minutes, and 47 sec« onds. Hence the sun's mean daily motion in longitude is found by the proportion One year : one" day : : 360° : 59
Page 292 - All the other stars of our firmament are apparently at a greater distance from us ; and if the distance of the nearest stars is so great, we must conclude that those faint stars which are barely discernible in powerful telescopes are much more distant. Hence we conclude that we do not see them as they now are, but as they were years ago ; perhaps, in some instances, with the rays which proceeded from them several thousands of years ago...
Page 128 - Join SC, and, because SB and Cc are parallel, the triangle SBC will be equal to the triangle SBc, and therefore also to the triangle SAB. By the like argument, if the centripetal force acts successively in C, D...
Page 55 - ... most curious effects of atmospheric refraction is the oval form of the disks of the sun and moon, when near the horizon. This arises from the unequal refraction of the upper and lower limbs. The latter being nearer the horizon is more affected by refraction, and therefore raised in a greater degree than the upper limb, the effect of which is to bring the two limbs apparently closer together, by the difference between the two refractions. The form of the disk is therefore affected as if it were...