I think, if A. E. B. will reconsider this opinion, he will find that, so far from being "greatly in excess," it is inadequate to account for the amount of apparent motion of the plane of the pendulum. For the onward motion of the plane of a 2 sec. pendulum, describing a circle of 10 feet diameter in twenty-four hours, amounts to ·0087 inch at each beat; 50 feet will be the difference in the distance the two extremities of the arc of vibration will travel in twenty-four hours; that is, ·0138 inch in 2 seconds of time: but this is for a difference of 10 feet; therefore, for 5 feet, the distance from the centre, it is ·0069 inch; whereas the arc described is ·0087 inch, which is absurd. However, there is another equally fatal objection to this theory, founded on experiment; to make which objection good, I will not merely adduce the result of my own, but that of certain experiments carried out at Paris, which place the matter beyond a doubt. In the Pantheon, at Paris, there is a pendulum of the length of 230 feet, by means of which experiments can be made under the most favourable conditions possible as regards suspension, exclusion of currents of air, &c. &c. While witnessing the trials that were being made, a relation of mine requested that the pendulum might be set to oscillate east and west; and the result was, that the arc described after an interval of ten minutes, was the same as that described when the pendulum was oscillating north and south. To return to the original theory. I stated formerly that I had no faith in the experiments which had been published. I now repeat that I believe all the experiments that have been made, with the view of showing the rotation of the earth, and the independence of the pendulum of that rotation, are inconclusive; and for the following reason, _the impossibility of obtaining perfect suspension_. Even in a still atmosphere, and with a pendulum formed of the rigid rod and a "bob," the axis of both of which shall be precisely in a line with the point of suspension; yet, until suspension can be effected on a mathematical point, and all torsion and local attraction got rid of, the pendulum will not continue to swing _in the same plane_ for many consecutive beats; because the _slightest_ disturbance will cause the "bob" to describe an ellipse; and, by a well-known law, the major axis of that ellipse will go on advancing in the direction of the revolution. This advance is by regular intervals; and my belief, founded on my own experiments, is, that the astonished spectators at the Polytechnic Institution, while intently watching, as they believed, the rotation of the earth made visible, were watching merely a weight suspended by a cord, which, disturbed from the plane in which it was set to oscillate, was describing a series of ellipses on the table, very pretty to look at, but having no more to do with the rotation of the earth than the benches on which they were sitting.