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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1863 Excerpt:... the parallax by observations of zenith-distance at different observations, by taking advantage of the fact that, owing to the excentricity of his orbit, he comes much nearer to us at some oppositions than at others, so near indeed that in some cases the horizontal parallax has amounted to as much as 22". For the purpose of giving greater efficiency to the use of this method, there is published in the Nautical Almanac, for each opposition of the planet, a list of stars situated so near his path as to be conveniently compared with him either by the use of meridian instruments or of an equatorial. The way in which the amount of parallax is deduced is sufficiently obvious. Thus, let z and z be as before the true meridian zenith-distances of the planet as affected with the parallaxes Pr sin z, and Pr sin z (and let the observation made at one station be reduced to the meridian of the other station, by the motion in N.P.D. of the planet in its passage from the more easterly to the more westerly meridian); let also zt and he the true meridian zenith-distances of the star observed at the two stations, and 7 and 7' the co-latitudes of the stations M. A. 13 194 OBSERVA TIONS OF N.P.D. OF MARS FOR PARALLAX. (the one referred to the North Pole and the other to the South Pole). Then the true geocentric N.P.D's of the planet will be 7 + z-Pr sin z, and 180-(7' + z-Pr sin z') and the N.P.D's of the stars will be 7 + z, and 180-(7' + «,'), and therefore the difference of N.P.D. of the planet and star, will be at the first station (the Cape for example) z--zt--Pr sin z, and at the second zt'--z' + Pr sin z'; and these must manifestly be equal. Hence P= g7' + a. r sin z + r sin z The advantage of this method is that it requires only the difference of meridian zeni...