Peak time

Still on the subject of time, in a recent edition of the Infinite Monkey Cage, I was surprised to hear Professor Brian Cox say "counter-clockwise", since I had taken it to be a term from US English. I assumed that it was because he must have spent no little time in the US, and presumably reads a lot of US literature. When I looked at the relative frequencies of "counter-clockwise" and "anti-clockwise" in the Google ngram viewer, I noticed something surprising:

Here's the chart for UK English - a closer battle than I would have expected, but with anti-clockwise just keeping a lead. However, there is a distinct peak in the 1940s, since when the use of both terms has been on the decline.

The peak is even more pronounced in American English. Counter-clockwise wins comfortably, but since 1940 has been in decline.

Why should this be? Perhaps as more stuff has been displayed digitally, and we are less in touch with making and repairing things by hand, the words for rotating something one way or the other are falling out of fashion.

This seems to be supported by a search for "clockwise", which is suffering a similar, if less marked, decline:

American English

British English

Finally, although I won't include the graphs, mentions of the pre-clock words "sunwise" (ie, clockwise) and particularly "widdershins" (ie, anti-clockwise) have tended to grow over the same period. I have no idea why.