Newton was of opinion that matter was made up, in the last resort, of exceedingly small solid particles, having no pores, or empty spaces within them. Priestley, in his Disquisitions relating to Matter and Spirit, carries the theory one step farther; and, as Newton surrounds his exceedingly small particles with spheres of attraction and repulsion, precluding in all cases their actual contact, Priestley is disposed to regard the centre of these spheres as mathematical points only. If there is no actual contact, then by the very terms no two particles of matter were ever so near to each other, but that they might be brought nearer, if a sufficient force could be applied for that purpose. You had only another sphere of repulsion to conquer; and, as there never is actual contact, the whole world is made up of one sphere of repulsion after another, without the possibility of ever arriving at an end. "The principles of the Newtonian philosophy," says our author, "were no sooner known, than it was seen how few in comparison, of the phenomena of nature, were owing to solid matter, and how much to powers, which were only supposed to accompany and surround the solid parts of matter. It has been asserted, and the assertion has never been disproved, that for any thing we know to the contrary, all the solid matter in the solar system might be contained within a nutshell(45)." (45) Priestley, Disquisitions, Section II. I know not by whom this illustration was first employed. Among other authors, I find, in Fielding (Joseph Andrews, Book II, Chap. II), a sect of philosophers spoken of, who "can reduce all the matter of the world into a nutshell."