Dr WHEWELL, ON PLATO'S SURVEY OF THE SCIENCES. 587 



detected the effect of universal gravitation. The realities which Plato looked for, as something 

 incomparably more real than the visible luminaries, are found, when we find geometrical 

 figures, epicycles and eccentrics, laws of motion and laws of force, which explain the appear- 

 ances. His Realities are Theories which account for the Phenomena, Ideas which connect the 

 Facts. 



But, is Plato right in holding that such Realities as these are more real than the 

 Phenomena, and constitute an Astronomy of a higher kind than that of mere Appearances ? 

 To this we shall, of course, reply that Theories and Facts have each their reality, but that 

 these are realities of different kinds. Kepler's Laws are as real as day and night ; the 

 force of gravity tending to the Sun is as real as the Sun ; but not more so. True 

 Theories and Facts are equally real, for true Theories are Facts, and Facts are familiar 

 Theories. Astronomy is, as Plato says, a series of Problems suggested by visible Things ; 

 and the Thoughts in our own minds which bring the solutions of these Problems, have a 

 reality in the Things which suggest them. 



But if we try, as Plato does, to separate and oppose to each other the Astronomy of 

 Appearances and the Astronomy of Theories, we attempt that which is impossible. There are 

 no Phenomena which do not exhibit some Law ; no Law can be conceived without Phenomena. 

 The heavens offer a series of Problems ; but however many of these Problems we solve, there 

 remain still innumerable of them unsolved ; and these unsolved Problems have solutions, and 

 are not different in kind from those of which the extant solution is most complete. 



Nor can we justly distinguish, with Plato, Astronomy into transient appearances and per- 

 manent truths. The theories of Astronomy are permanent, and are manifested in a series of 

 changes: but the change is perpetual just because the theory is permanent. The perpetual 

 change is the permanent theory. The perpetual changes in the positions and movements of 

 the planets, for instance, manifest the permanent machinery : the machinery of cycles and epi- 

 cycles, as Plato would have said, and as Copernicus would have agreed ; while Kepler, with a 

 profound admiration for both, would have asserted that the motions might be represented by 

 ellipses, more exactly, if not more truly. The cycles and epicycles, or the ellipses, are as real 

 as space and time, in which the motions take place. But we cannot justly say that space and 

 time and motion are more real than the bodies which move in space and time, or than the 

 appearances which these bodies present. 



Thus Plato, with his tendency to exalt Ideas above Facts, — to find a Reality which is more 

 real than Phenomena, — to take hold of a permanent Truth which is more true than truths of 

 observation,' — attempts what is impossible. He tries to separate the poles of the Fundamental 

 Antithesis, which, however antithetical, are inseparable. 



At the same time, we must recollect that this tendency to find a Reality which is some- 

 thing beyond appearance, a permanence which is involved in the changes, is the genuine spring 

 of scientific discovery. Such a tendency has been the cause of all the astronomical science 

 which we possess. It appeared in Plato himself, in Hipparchus, in Ptolemy, in Copernicus, 

 and most eminently in Kepler ; and in him perhaps in a manner more accordant with Plato's 

 aspirations when he found the five Regular Solids in the Universe, than when he found there 

 the Conic Sections which determine the form of the planetary orbits. The pursuit of this 

 tendency has been the source of the mighty and successful labours of succeeding astronomers : 



