"Such is the scene seen at right angles with the plane in which the planets move; but what would be its aspect if I saw it in the line of the plane? What would be its appearance if I saw it edgewise? There arises in my mind one of those uncertainties which so frequently convince me that I am ignorant. I cannot complete my picture, for I do not know whether all the planets move in one plane. How determine the point? A ray of light breaks in. Huzza! I have found it. If the courses of the planets as seen in the heavens form parallel lines, then must they all move in one plane; and _vice versa_. But hold! That would be as seen from the sun--if the planets _could_ be seen from the sun. The earth is but one of their own number, and from it the point of view must be disadvantageous. The diurnal motion must perplex. But no. The apparent motion of the heavens need not disturb the observation. Let the course of the planets through the fixed stars, be marked, and though, from the peculiarity of the point of observation, their motion may at one time seem more rapid, and at another more slow, yet, if their plane be, as a workman would say, _out of twist_, their lines will seem parallel. Still in some doubt, however: I long for a glance at an Orrery, to determine the point; and then I remember that Ferguson, an untaught man like myself, had made more Orreries than any one else, and that mechanical contrivances of the kind were the natural recourse of a man unskilled in the higher geometry. But it would be better to be a mathematician than skilful in contriving Orreries. A man of the Newtonian cast of mind, and accomplished in the Newtonian learning, could solve the problem where I sat, without an Orrery. "From the thing contemplated, I pass to the consideration of the mind that contemplates. Oh! that wonderful Newton, respecting whom the Frenchman inquired whether he ate and slept like other men! I consider how one mind excels another; nay, how one man excels a thousand; and, by way of illustration, I bethink me of the mode of valuing diamonds. A single diamond that weighs fifty carats is deemed more valuable than two thousand diamonds, each of which only weighs one. My illustration refers exclusively to the native powers; but may it not, I ask, bear also on the acquisition of knowledge? Every new idea added to the stock already collected is a carat added to the diamond; for it is not only valuable in itself, but it also increases the value of all the others, by giving to each of them a new link of association.