in so far as it was universal. Otherwise it presents few qualities to which we should attach this name at present. For the system contemplated the division of matter into separate parts, each of which occupied a place—a place subject to change, no doubt—in empty space, while to these circling orbs force was linked somehow. The relation between any two, therefore, can not be the result of inherent nature, but must follow from the interference of a cause external to the terms of the relation. Newton has put himself on decided record on this very question. In a letter to Bentley, written about the new year of 1693, he says: "It is inconceivable that inanimate brute matter should, without the mediation of something else, which is not material, operate upon and effect other matter without mutual contact, as it must be, if gravitation, in the sense of Epicurus, be essential and inherent in it. And this is one reason why I desired you would not ascribe innate gravity to me. That gravity should be innate, inherent and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to the other, is to me so great an absurdity that I believe no man, who has in philosophical matters a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers." Summarily put, this means that the solar system is the type of universe, and it is a system, because 'an agent acting constantly according to certain laws' has rendered it such. And this implies, further, that, while a description of the universe may be possible, as in terms of mathematics, an explanation of it is beyond reach.
Turning to the philosophical side, a curious parallelism attracts notice at once. Of course, we are dealing no longer with 'heavenly bodies,' but matter and mind are treated by the philosophers exactly as Newton dealt with his material wholes. Descartes asks himself in effect. How is it that thought, which possesses none of the qualities of extension (matter) and extension, which possesses none of the qualities of thought, comes to unite so as to be a single whole in man's experience? He supposes that ideas are copies of things. But, even so. How do we know that the copies are correct or reasonably adequate? The solution can come by one answer alone. Some agent, which is neither an idea nor a thing, must vouch for the correspondence. Just as, in the physical world, one body can not affect another, except by the operation of a law-giving agent, so thought and extension can not be combined in our universe, except God have so willed it. The parallelism is precise. A 'third thing,' belonging neither to the sphere of intellect nor to that of the external world, must be assumed as the
