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Before circa 1970, it was more common to say "kilocycles" than "kilohertz" (and analogously for "mega-," "giga-," etc.). What contributed to "Hertz" becoming more common than "cycles"?

cf. the Google Ngram graph for "megahertz,megacycles,kilocycles,kilohertz,gigacycles,gigahertz"

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    $\begingroup$ Officially in 1960. However, I vaguely remember some reference to that new standard in the late 1950s… $\endgroup$
    – J. C . Nocker
    Oct 23, 2021 at 11:00
  • $\begingroup$ I left the RN in 1973 and Megacycles and Kilocycles were certainly used officially both verbally and in documentation. I was in radio communications and Hertz was unheard of. So it certainly took the military some time before adopting the use of Hertz. $\endgroup$
    – Terence Corney
    Nov 12, 2021 at 23:57

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SI units started to be used.

In 1960 (not 1970!), the Système international d'unités was established at the General Conference on Weights and Measures. The hertz was officially recognized as a unit derived from metric system units (namely, the second). It was already in partial use (the International Electrotechnical Commission began using it in 1930). With the rise of the hertz, the phrase "cycles" in "cycles per second" fell out of fashion, leading to the general trend we see on the Google Ngram.

Interestingly enough, adding "hertz" to the Ngram search shows that its usage, too, took off a bit after 1960, though it was already fairly popular.

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  • $\begingroup$ Ah, good distinction: "started to be used". SI units are much older than 1960. $\endgroup$
    – Geremia
    Jan 7, 2017 at 22:31
  • $\begingroup$ If you add "kHz" and "MHz" to your ngram search, you'll see they take off sooner and much, much more dramatically than "kilohertz" and "megahertz". $\endgroup$
    – Russell Borogove
    Jan 8, 2017 at 2:13
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The General Conference on Weights and Measures (1960) adopted the herz unit. So you have found that it took about 10 years for English-speaking books to catch up with that change.

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There was indeed some resistance to adopting the new name in the United States. In 1967, Rufus Cartwright wrote about it in the magazine ``Electronic Illustrated":

Is the short, illustrious life of Heinrich Hertz any reason to change the English language? A quick answer is no, especially since hertzian waves and antennas already honor him. But that may be the short view. Perhaps we must take the long view and see life as a complete hertz.

What might have helped in popularizing the new unit is that saying 'cycle' is potentially confusing when 'cycle per second' is really meant.

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  • $\begingroup$ An older physicist once told me he had a most FRUSTRATING experience in discussing a phase-locked loop, when he noted that the locked loop was different from the reference by a quarter cycle... and was immediately interrupted by an excited engineer who said the frequencies couldn't be tolerated to be so different. $\endgroup$
    – Whit3rd
    Jan 18, 2017 at 9:51
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    $\begingroup$ I do wonder if this again a language/national issue, as the UK/US world was slow to adopt international units. As far as I know, in Germany Hz was common since the 1930s. Here is e.g. an instrument from about 1950 that has the words "500 Hz" written on the scale: alte-messgeraete.de/elektrotechnik/ddr-produktionen/multizet There isn't even a good equivalent word to the English "cycles" in German; one can say "Schwingungen pro Sekunde" but that's rather unpractical. $\endgroup$
    – Stephan Matthiesen
    Oct 31, 2021 at 12:00

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