Gaël sent an interesting reference:

Hi Jeroen, Have you heard of Galton’s measurement of boredom with fidgets?
“Many mental processes admit of being roughly measured. For instance, the degree to which people are bored, by counting the number of their fidgets. I not infrequently tried this method at the meetings of the Royal Geographical Society, for even there dull memoirs are occasionally read. […] The use of a watch attracts attention, so I reckon time by the number of my breathings, of which there are 15 in a minute. They are not counted mentally, but are punctuated by pressing with 15 fingers successively. The counting is reserved for the fidgets. These observations should be confined to persons of middle age. Children are rarely still, while elderly philosophers will sometimes remain rigid for minutes altogether.”
The text apparently comes from his “memories of life” but many references to it can be found on the web and on Google Books. Kind regards, Gaël

Here is the fragment quoted in the book ‘Boredom: The Literary History of a State of Mind’ by Patricia Meyer Spacks.

Apparently, I was not the first to use the word ‘fidgets’ in a scientific context. How sad and how wonderful. I think I should read a bit more about Francis Galton. Hmm, first impressions: what a giant of a man… As far as interest in fidgeting goes, I seem to be in good company 🙂