It is then with senses, from the impressions upon which we are impelled to draw such false conclusions, and that present us with images altogether unlike any thing that exists out of ourselves, that we come to observe the phenomena of what we call the universe. The first observation that it is here incumbent on us to make, and which we ought to keep ever at hand, to be applied as occasion may offer, is the well known aphorism of Socrates, that "we know only this, that we know nothing." We have no compass to guide us through the pathless waters of science; we have no revelation, at least on the subject of astronomy, and of the unnumbered inhabitable worlds that float in the ocean of ether; and we are bound therefore to sail, as the mariners of ancient times sailed, always within sight of land. One of the earliest maxims of ordinary prudence, is that we ought ever to correct the reports of one sense by the assistance of another sense. The things we here speak of are not matters of faith; and in them therefore it is but reason, that we should imitate the conduct of Didymus the apostle, who said, "Except I put my fingers into the prints of the nails, and thrust my hand into his side, I will not believe." My eyes report to me an object, as having a certain magnitude, texture, and roughness or smoothness; but I require that my hands should confirm to me the evidence of my eyes. I see something that appears to be an island at an uncertain distance from the shore; but, if I am actuated by a laudable curiosity, and wish to possess a real knowledge, I take a boat, and proceed to ascertain by nearer inspection, whether that which I imagined to be an island is an island or no. There are indeed many objects with which we are conversant, that are in so various ways similar to each other, that, after having carefully examined a few, we are satisfied upon slighter investigation to admit the dimensions and character of others. Thus, having measured with a quadrant the height of a tower, and found on the narrowest search and comparison that the report of my instrument was right, I yield credit to this process in another instance, without being at the trouble to verify its results in any more elaborate method.