A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . s and CD the conjugate of the ellipse such a process of elongating the circle into an el-lipse, the center of the circle may be conceived of asdrawn opposite ways to E and F, each of which be-comes a focus, and both together are called the foci of theellipse. The distance G£ or GF of the focus from the 128. Recite the first law. In a circle, how are all the diam-eters 1 How are they in
A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . s and CD the conjugate of the ellipse such a process of elongating the circle into an el-lipse, the center of the circle may be conceived of asdrawn opposite ways to E and F, each of which be-comes a focus, and both together are called the foci of theellipse. The distance G£ or GF of the focus from the 128. Recite the first law. In a circle, how are all the diam-eters 1 How are they in an ellipse ? What is the longest di-ameter called 1 What is the shortest called ? Explain by figure26. What is the eccentricity of the ellipse ? How many el-lipses may there be having a common focus 1 Explain figure2§ How eccentric is the earths orbit ? 100 UNIVERSAL GRAVITATION. center is called the eccentricity of the ellipse ; and theellipse is said to be more or less eccentric, as the distanceof the focus from the center is greater or less. Now there may be an indefinite number of ellipseshaving one common focus, but varying greatly in ec-centricity. Figure 27 represents such a collection of. ellipses around the common focus F, the innermost AGDhaving a small eccentricity or varying little from a cir-cle, while the outermost ACB is a very eccentric orbits of all the bodies that revolve about the sun,both planets and comets, have, in like manner, a com-mon focus in which the sun is situated, but they differin eccentricity. Most of the planets have orbits of very little eccen-tricity, differing little from circles, but comets move invery eccentric ellipses. The earths path around the sun varies so little froma circle, that a diagram representing it truly wouldscarcely be distinguished from a perfect circle ; yetwhen the comparative distances of the sun from theearth are taken at different seasons of the year, as is ex-plained m Art. 118, we find that the differe
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
