Although nothing, to minds capable of comprehending it, can add to the force or clearness of the demonstration by which the rotation of the earth has been established, yet even the natural philosopher himself cannot regard the present experiment without feelings of profound interest and satisfaction; and to the great mass, to whom the complicated physical phenomena by which the rotation of the earth has been established are incomprehensible, M. Foucault's very ingenious illustration is invaluable. A correspondent of the Newark _Daily Advertiser_ appears to have anticipated the experiment of M. Foucault, suspending a fifty-six pound weight by a small wire from the rafters of a barn. But however simple and conclusive the illustration, it should be attempted only by scientific men. Professor Sylvester, writing to the _Times_, of experiments made in London, says: "The experiments connected with the practical demonstration of the phenomenon require to be conducted with great care; and some discredit has been brought upon attempts to illustrate it in England by persons who have not taken the necessary precautions to protect the motion from the excentric deviation to which it is liable, and which may, and indeed must, have the effect of causing, in some cases, an apparent failure, and in others a still more unfortunate, because fallacious, success. I believe, from the character of the persons connected with the experiments, that the true phenomenon has been accurately produced and observed in Paris. I doubt whether as much can be said, with entire confidence, of any of the experiments hitherto performed here in London. "Any want of symmetry in the arrangements for the suspension of the wire, or in the centering of the weight, exposure to currents of air, or the tremulous motion occasioned by the passage of vehicles, may operate to cause a phenomenon to be brought about curious enough in itself, as a result of mathematical laws, but quite different from that supposed. The phenomenon of the progression of the apsides of an oval orbit, which is here alluded to, is familiar to all students in mechanics.