Arithmetica et Geometria practica. By Adrian Metius. Leyden, 1640, 4to.[168] This book contains the celebrated approximation _guessed at_ by his father, Peter Metius,[169] namely that the diameter is {100} to the circumference as 113 to 355. The error is at the rate of about a foot in 2,000 miles. Peter Metius, having his attention called to the subject by the false quadrature of Duchesne, found that the ratio lay between 333/106 and 377/120. He then took the liberty of taking the mean of both numerators and denominators, giving 355/113. He had no right to presume that this mean was better than either of the extremes; nor does it appear positively that he did so. He published nothing; but his son Adrian,[170] when Van Ceulen's work showed how near his father's result came to the truth, first made it known in the work above. (See _Eng. Cyclop._, art. "Quadrature.") ON INHABITABLE PLANETS. A discourse concerning a new world and another planet, in two books. London, 1640, 8vo.[171] Cosmotheoros: or conjectures concerning the planetary worlds and their inhabitants. Written in Latin, by Christianus Huyghens. This translation was first published in 1698. Glasgow, 1757, 8vo. [The original is also of 1698.][172] The first work is by Bishop Wilkins, being the third edition, [first in 1638] of the first book, "That the Moon may be a Planet"; and the first edition of the second work, {101} "That the Earth may be a Planet." [See more under the reprint of 1802.] Whether other planets be inhabited or not, that is, crowded with organisations some of them having consciousness, is not for me to decide; but I should be much surprised if, on going to one of them, I should find it otherwise. The whole dispute tacitly assumes that, if the stars and planets be inhabited, it must be by things of which we can form some idea. But for aught we know, what number of such bodies there are, so many organisms may there be, of which we have no way of thinking nor of speaking. This is seldom remembered. In like manner it is usually forgotten that the _matter_ of other planets may be of different chemistry from ours. There may be no oxygen and hydrogen in Jupiter, which may have _gens_ of its own.[173] But this must not be said: it would limit the omniscience of the _a priori_ school of physical inquirers, the larger half of the whole, and would be very _unphilosophical_. Nine-tenths of my best paradoxers come out from among this larger half, because they are just a little more than of it at their entrance. There was a discussion on the subject some years ago, which began with The plurality of worlds: an Essay. London, 1853, 8vo. [By Dr. Wm. Whewell, Master of Trinity College, Cambridge]. A dialogue on the plurality of worlds, being a supplement to the Essay on that subject. [First found in the second edition, 1854; removed to the end in subsequent editions, and separate copies issued.][174]