PHYSICS. 345 



for producing- beat-tones. It consists of two glass rods or tubes of dif- 

 ferent lengths clamped vertically at tbeir centers to a jointed frame. 

 By means of an elastic band their lower ends are pressed against the 

 periphery of a wheel covered with cloth and dipping into water. The 

 longitudinal vibration produ(;ed when the wheel is turned is strong and 

 the beat-tones are very distinct. {Wied. Ann., 1881, II, xii, 350.) 



Maschke has devised a simple form of apparatus for showing the 

 nodal points in tubes. A wooden graduated scale has a groove along 

 its upper surface, on which is placed a glass tube. At one end a small 

 steel rod is supported which enters the tube and carries at its extrem- 

 ity a ring covered with a membrane. Against this hangs a small ball 

 of shellac, suspended by a silk fiber from the upper edge of the ring. 

 If the air within the tube be vibrated by any suitable means, as by a 

 tuning fork, the ball is thrown into vibration, if placed at a loop, but 

 remains at rest when at a node. The effects may be projected on a 

 screen. {Wied. Ann., 1881, II, xiii, 204.) 



Koenig has also contrived a method for exploring the interior of organ- 

 inpes while in action without interfering with their operation. The 

 I)ipe used has a front of plate glass, graduated, and a longitudinal slit 

 at the back. It is jilaced horizontally in a trough so that the slit and 

 half of the back are below the surface of the water which it contains. A 

 thin brass tube bent twice at right angles is supported so that one end 

 enters the slit to about the middle of the jjipe. It can be slid along the 

 pipe, and is connected by a rubber tube either with the ear or a mono- 

 metric flame capsule. When the inner end of the tube passes a ventral 

 segment in the i^ipe a sudden weakening of the sound is noticed, and 

 then a sudden strengthening. In this way the position of the nodes and 

 segments can be exactly ascertained. The results are not in exact ac- 

 cord with theory. ( Wied. Ann., 1881, II, xiii, 569.) 



Lovering has discovered a paper communicated to the American 

 Academy by Nathaniel Bowditch in 1815, in which he investigates the 

 figures made by a double pendulum which compounded two vibrations 

 at right angles with one another. The text is illustrated by several 

 plates of figures, which prove clearly the anticipation of the figures given 

 by Lissajons in 1857. The ratios investigated were unison, octave, 

 twelfth, and the double octave. {Proc. Am. Acad., .) 



Crova has described an apparatus for recording Lissajous's curves 

 mechanically. It consists of a pendulum of wire with a heavy weight 

 suspended from the ceiling and carrying a brush dipped in ink. Be- 

 neath this is a curved table attached to the toj) of a second pendulum 

 formed of a rod, vibrating on knife-edges in a plane at right angles to 

 the first, and carrying an adjustable weight below. The ai)i>aratus used 

 by Crova has an upper i)endulum 0.7 meters long vibrating in 2.0 seconds, 

 and the figures are inscribed in a square 0.25 meter on a side. By burn- 

 ing a thread which holds the up])er pendulum at any particular i)hase, 

 the resultant curve is described on the paper covering the curved table. 

 {J. Phys., May, 1881, x, 211.) 



