Two types of whistles will be described which have been useful as high power sources for work in atmospheric ultrasonics. The first has an annular windway, an annular lip and cavity; weighs 2.5 oz.; is capable of delivering 0.1 watt at mouth blowing pressure and 10 watts when the pressure drop across the whistle is 8 lb./sq. in., and the air flow is 10 cu.ft./min. The second weighs 0.5 oz.; puts out 0.005 watt when mouth blown, and 0.5 watt when the airflow is 0.5 cu.ft./min., for a gauge pressure of 20 lb./sq. in. An experimental study of ultrasonic whistles has been carried out to discover how the intensity and frequency of their output depends upon their dimensions and upon the airflow. The relationships noted can be explained qualitatively by assuming that the whistle is a system of two oscillators, the first being the air in the cavity, and the second the “jet and edge,” which functions as driver and produces edge tones having properties similar to those observed by Brown in his studies of edge tones of lower frequencies and at lower air velocities.