ULTRASONICS — LAUFER 217 



becomes too short for practical use, limiting the output of this gen- 

 erator to a maximum frequency of about 60 kilocycles. For higher 

 frequencies the piezoelectric generator has no contender. 



It was not until 1930 that noninilitary ultrasonic research received 

 its first real impetus as the result of the work of R. AV. Wood and 

 A. L. Loomis. Wood, who attributed his interest in the subject to 

 the demonstrations he witnessed in Langevin's laboratory at Toulon, 

 imbued Loomis with his own enthusiasm. Alfred Loomis, a wealthy 

 amateur (in the French sense of the word) in the physical sciences, 

 helped Wood set up an elaborate laboratory at Tuxedo Park, N. Y., 

 where they undertook the first serious, comprehensive study of the 

 physical and biological effects of ultrasonic radiation. 



Their apparatus consisted of a disk of quartz resting upon a lead 

 plate at the bottom of a shallow dish filled with transformer oil. The 

 upper surface of the quartz was covered by a thin metal foil, and the 

 foil and the lead plate were connected to the output of a 2-kilowatt 

 vacuum-tube oscillator. The oscillator was an imposing affair indeed ! 

 Consisting of two huge Pliotron tubes, a huge bank of oil condensers, 

 a variable condenser 6 feet high and 2 feet in diameter, and an induc- 

 tion coil, it delivered upwards of 50,000 alternating volts to the quartz 

 transducer. 



When the quartz was excited near its resonant frequency, a mound 

 of oil was raised several centimeters above the oil level in the dish 

 and appeared to be in violent agitation. A thermometer immersed 

 in the oil showed only a moderate rise in temparature, but a finger 

 immersed in the oil experienced a scalding pain of considerable 

 severity. When a test tube containing paraffin and water was held 

 in the oil bath, a rapid dispersion of the paraffin in the water took 

 place, yielding a suspension of unusual permanence. Blood corpus- 

 cles and other cells of animal or vegetable tissues immersed in a bath 

 in contact with the oil were violently disrupted, and frogs and 

 small fish were quickly killed. A tapering glass rod, half a milli- 

 meter in diameter at the tip, with its butt immersed in the oil, trans- 

 mitted ultrasonic vibrations of such intensity that a chip of wood 

 smoked and emitted sparks when pressed against the tip, the rod 

 burning its way rapidly through the wood. If a glass plate was 

 substituted for the wood, the rod drilled its way through the plate 

 throwing out the displaced material in the form of a fine powder or 

 minute fused globules of glass. The heating occurred only at the 

 point of contact, the remainder of the glass rod being quite cold. 

 These and a host of other new and interesting effects discovered by 

 Wood and Loomis pointed out the path which has since led into fields 

 of the most surprising variety, interest, and practical importance. 



