telescope so that it can point only to tins small portion of the sky. He draws an imaginary circle, called a meridian, and he will study the deportment of the stars only at the moment of crossing this line. He stations himself at this ideal barrier, and before allowing any stellar traveller to pass, he questions him minutely to determine his identity—the two essential points being, the time of day when he passes, and his distance north or south from the equator. He questions him on these points, because, if any discrepancy occurs on the occasion of any future transit, it is sure to bring out the secrets of his history. But how is the time-questioning effected? Put your eye to the telescope, and the process will at once be revealed to you. You are surprised, when you look in, to see a blaze of light, instead of darkness, as you expected. The light proceeds from a lamp, and its design is, to shew you clearly a slender kind of grating spread over the field of view. This consists of seven spiders' threads, stretched up and down at equal distances, and one crossing in the middle. The perpendicular line in the middle corresponds to the imaginary meridian line. You soon discover a star coming in at one side of the field of view, and, to your surprise, marching rapidly across the lines to the other side. The rapidity invariably startles when first observed; and it affords the most sensible proof of the motion of the earth. No doubt, you can persuade yourself of this motion by watching the heavens during any
