Underwater communication between ships, detection and location of approaching vessels, and echo-sounding of the ocean depths are expected to be some of the useful results which will be facilitated by the experiments now being carries on at the Crufts High Tension Laboratory by George W. Pierce, Rumford Professor of Physics and Director of the Laboratory. Assisted by Dr. Noyes, and Miss Prouty, Professor Pierce has been engaged in the investigation of supersonic noises in nature, or those noises made by small animals and insects at frequencies over 18,000 per second, the upper limit of the human ear.
Previous to this series of experiments no adequate methods existed for the study of these supersonic sounds, but recent work at the Crufts Laboratory has led to the development of apparatus making use of magnetostriction and Piezoelectric controlled oscillators and detectors.
Insect noises are not produced vocally, but are made by friction of one part of the body against another, by vibrations of the wings, by vibration of a muscularly controlled diaphragm, or by hitting the body against some external object.
At present a number of small, dark brown crickets, known as Nemobius Fasciatus, are kept in the Laboratory, and all the various sounds which they can make are being studied in detail.
These small, dark brown crickets have, however, a special sort of wing covers or tegmina, useless for flight, but used for producing its song. The under surface of the wing is covered with minute, (148 per millimeter) file-like projections which are scraped by a hardened, raised portion on the inner edge of the tegmina. The cricket draws this scraper edge across the rough under-part of the wing cover at a rate of 16 1-3 times per second, if the complete back and forth wing movement is counted as one, rather than as two, motions.
Scraping at this rate the bug can manage to produce a sound with a frequency of about 8,000 vibrations per second, or a note five octaves above middle C, but he can also go up to 16,000 and even 32,000 without ill effects. A rise in the temperature of the room in which he is being tested will cause a corresponding increase in the sound pulsations of his fiddling, putting the tempo up from 16 per second at 70 degrees Fahrenheit, to 20 beats a second at 94 degrees Fareneit. Only a male cricket can make these noises, since the female has no scratcher.
Professor Pierce has also listened to other noises besides crickets', including the song of newly-hatched robins, which he reports to be longest at 15,000 vibrations per second, and the black pole warbler which emits sounds at about 15,000 per second. The ultimate object of this series of experiments is to study and classify the sounds in nature and if possible to determine whether or not they serve for communication.