| 
 Observing waves formed by an oscillating rod |  | 
|   | The waves emanate from the source at an angle
        prescribed by the period of oscillation in only four
        directions. At a period shorter than the Brunt-Väisälä frequency, waves do not occur. | 
Experimental conditions
Brunt-Väisälä frequency: 3.9 sec.
Amplitude of the rod: approx. 0.5cmPhotographic conditions
f=135mm, F4.5, 1/15 seconds, ASA400, 2mm slit used.
Filming conditions
5mm slit used.
Speeded up 10 times.
240x180:15fps, 320x240:30fps