Whistlers
Helliwell's greatest discovery was accidental, as is often the case in science. Helliwell and one of his students, Jack Mallinckrodt, were investigating lightning noise at very low radio frequencies at Stanford University in 1950. Mallinckrodt heard some whistling sounds and brought them to Helliwell's attention. As Helliwell recalled in an article in the October 1982, issue of the Stanford Engineer, he thought it was an artifact, but he stood radio watch with Mallinckrodt until he heard these whistlers for himself. Helliwell described these sounds as "weird, strange and unbelievable as flying saucers" in a 1954 article in the Palo Alto Times.
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