make sure that the water had attained its ultimate velocity. The f rotation was indicated by a pointer affixed to a small stand resting ( bottom of the basin and rising slightly above the level of the water.
The pendulum (fig. 2), of which the lower part was immersec supported on two points (A, B) so that the possible vibrations were 1: to one vertical plane. In the usual arrangement the vibrations of tl would be radial, i.e. transverse to the motion of the water, but it was e turn the pendulum round when it was desired to test whether a circumfe] vibration could be maintained. The rod 0 itself was of brass tube 8 in diameter, and to it was clamped a hollow cylinder of lead D. Th<
of complete vibration (r) was about half a second. When it was desi; change the diameter of the immersed part, the rod C was drawn up 1 and prolonged below by an additional piece—a change which did not affect the period T. In all cases the length of the part immerse* about 6 cm.
Preliminary observations showed that in no case were vibrations gen< when the pendulum was so mounted that the motion of the rod won circumferential, viz. in the direction of the stream, agreeably to wha been found for the seolian harp. In what follows the vibrations, if an radial, that is transverse to the stream.
In conducting a set of observations it was found convenient to begin the highest speed, passing after a sufficient time to the next lower, andhands until the rotation was iform with passage of one or- two spokes in correspondence with an assigned .mber of beats. It was necessary to allow several minutes in order to