skillful combination of the altered distances and angles of position,* the elements of these orbits may be found, conclusions drawn regarding the absolute distance of the double stars from the Earth, and comparisons made between their mass and that of the Sun. [footnote] *Savary, in the 'Connaissance des Tems', 1830, p. 56 and 163. Encke, 'Berl. Jahrb.', 1832, s. 253, etc. Arago, in the 'Annuaire' 1834, p. 260, 295. John Herschel, in the 'Memoirs of the Astronom. Soc.', vol. v., p. 171. Whether, however, here and in our solar system, quantity of matter is the only standard of the amount of attractive force, or whether 'specific' forces of attraction proportionate to the mass may not at the same time come into operation, as Bessel was the first to conjecture, are questions p 148 whose practical solution must be left to future ages.* [footnote] * Bessel, 'Untersuchung. des Theils der planetarischen Storungen, welche aus der Bewegung der Sonne entstchen' (An Investigation of the portion of the Planetary Disturbances depending on the motion of the Sun) in 'Abh. der Berl. Akad. der Wissensch.', 1824 (Mathem. Classe), s. 2-6. The question has been raised by John Tobias Mayer, in 'Comment. Soc. Reg. Gotting.', 1804-1808, vol. xvi., p. 31-68. When we compare our Sun with the other fixed stars, that is, with other self-luminous Suns in the lenticular starry stratum of which our system forms a part, we find, at least in the case of some, that channels are opened to us, which may lead, at all events, to an 'approximate' and limited knowledge of their relative distances, volumes, and masses, and of the velocities of their translatory motion. If we assume the distance of Uranus from the Sun to be nineteen times that of the Earth, that is to say, nineteen times as great as that of the Sun from the Earth, the central body of our planetary system will be 11,900 times the distance of Uranus from the star 'a' in the constellation Centaur, almost 31,300 from 61 Cygni, and 41,600 from Vega in the constellation Lyra. The comparison of the volume of the Sun with that of the fixed stars of the first magnitude is dependent upon the apparent diameter of the latter bodies -- an extremely undertain optical element. If even we assume, with Herschel, that the apparent diameter of Arcturus is only a tenth part of a second, it still follows that the true diameter of this star is eleven times greater than that of the Sun.* [footnote] *'Philos. Trans.' for 1803, p. 225. Arago, in the 'Annuaire', 1842, p. 375. In order to obtain a clearer idea of the distances ascribed in a rather earlier part of the text to the fixed stars, let us assume that the Earth is a distance of one foot from the Sun; Uranus is then 19 feet, and Vega Lyrae is 158 geographical miles from it.