we must know the longitudes of those points. We indeed/ ywhat has preceded, already know them to a certain degree oexactness, since in page 454, the longitude of the apogeewas found to be nearly 8* 8° 55' Q,"A. After we have discusseKepler’s problem, we will devise more exact methods o^determining the place of the apogee. The place of eapogee being determined, there will arise a question con^cerning the permanency of that place in the Heavens. I* 11 epreceding instance (see p. 447.) the longitude of the apog eewas found for the year 1775. Will it be the same for any otepoch ? The obvious method of solving this question will be 0find, for two different epochs, by the same process, the long 1tudes of the apogee. The results wilt shew whether the apog eebe stationary, progressive, or regressive.

The place of the apogee being known for any given epoch,and the law of its translation, the place may be determined orany other epoch ; and thence, since Kepler’s problem determine 8the body’s place in the ellipse, we shall be able to determine t eSun’s place or longitude for any assigned epoch. This it isobject of Solar Tables to effect. If tbeir elements be correct,they enable us to assign the Sun’s longitude for years that are tocome. But the elements of the Tables stand in need of frequentrevision : for, the dimensions of the solar ellipse, from the actionof the planets, are continually varying, and, which is a reasonof a different sort, our means of determining the dimension 8become, from the advancement of science and art, progressive 'better. If, therefore, the construction of solar and planetaryTables be our first object, their correction will be the second-