Circles 3 and 4, 4 and 5, 6 and 7, and 7 and 8 ought to produce as many beats as circle 1 produces simple shocks; and circles 3 and 5, 6 and 8, as many beats as circle 2 produces simple shocks; but we must content ourselves in these experiments with a much less perfect result, for the following reasons: The disk never being rigorously plane, alternately approaches the single wind pipe and recedes from it. No matter how slight this deviation is, every sound given by a single circle is heard with periodical intensities which complicate the phenomenon. This inconvenience could be avoided by placing several wind-pipes around the circle; but while we can extend the period of the holes in two circles (whose difference is 1) around the whole circle by blowing through a single wind tube, we would be compelled to limit it to the distance between two wind tubes, and it would become too short; for, when the disk rotates with a velocity sufficient to produce notes high enough and intense enough, the beats become too numerous to be easily perceived. Besides these provisions, which sufficiently illustrate the points to which we desire to call especial attention, Koenig also furnishes two more disks. The seventh contains 8 circles having 48, 54, 60, 64, 72, 80, 90, and 96 holes respectively. The 1st, 3d, 5th, and 8th will produce a perfect chord when the air is admitted through the 11 holes in the wind chest; with one wind tube the entire gamut may be obtained. Finally the eighth disk contains 8 circles of holes, whose numbers are in the ratio of 1:2:3:4, etc., and which may be used to illustrate harmonics. C. F. K. * * * * * THE MOTIONS OF CAMPHOR UPON THE SURFACE OF WATER. [Footnote: Continued from SUPPLEMENT No. 391, page 6240.] To have these movements occur in a constant and invariable manner upon the surface of water, and especially upon mercury, it is necessary to take precautions in regard to cleanliness, this being something that we have purposely neglected to mention to our readers. For we wished, through this voluntary omission, to stimulate their sagacity by bringing them face to face with difficulties that they will perhaps have succeeded in overcoming, with causes of error that they will have perceived, and the principal one of which is the want of absolute cleanliness in the water, vessels, and instruments that they may have used for the experiments.