set spinning obliquely, it will be seen that the axis will continue to point along the line it took at the commencement of motion. By placing a heavy sphere in a lathe, resting its projecting axial points on some moveable bearings, and then getting the sphere into extremely rapid motion, one of the bearings may be removed without the mass falling to the ground. The rapidity of motion changes so constantly and quickly the position of the particles which have a tendency to fall, that we have motion balanced against the force of gravitation in a striking manner; and we learn, from this experiment, the explanation of the planetary and stellar masses revolving on their axis at a speed sufficient to maintain them without support in space. A mass of matter, a sphere or a disc, carefully balanced, is fixed in gymbals such as we employ for fixing our compass needles, and it is set by some mechanical contrivance in rapid rotation. The position of the axis of rotation remains unaltered, although the earth is moving; and thus, by this instrument,--called the gyroscope,--we can determine, as with the pendulum, the motion of the earth around its axis; and we learn why, during its movement around the sun, its axis is undeviatingly pointed towards one point in space, marked in our Heavens as the Polar Star. In addition to these great rotations, the earth is subjected to other motions, as the precession of the equinoxes and the nutation of its axis. Rocking regularly upon a point round which it rapidly revolves, whilst it progresses onward in its orbit, like some huge top in tremulous gyration upon the deck of a vast aërial ship gliding rapidly through space, is the earth performing its part in the great law of motion. The rapidity of these impulses, supposing the powers of the physical forces were for a moment suspended, would be sufficient to scatter the mass of our planet over space as a mere star-dust. Limiting, as much as possible, the view which opens upon the mind as we contemplate the adjustments by which this great machine, our system, is preserved in all its order and beauty, let us forget the great movement of the whole through space, and endeavour to consider the effect of those motions which are directly related to the earth, as a member of one small group of worlds. We cannot for a moment doubt, although we have not any experimental proof of the fact, that the proper motions of the earth materially influence the conditions of the matter of which it is formed. Every pair of atoms is, like a balance, delicately suspended, under the constant struggle which arises from the tendency to fly asunder, induced by one order of forces--centrifugal force--and the efforts of others, gravitation and cohesion, to chain them together. The spring is brought to the highest state of tension--one tremor more, and it would be destroyed.