Slightly massaged version of the data located by Sempaiscuba in this Google Sheet. There were a few errors in the data. I used it to produce this chart of US Congress days in session per year:
Some counts are off because I didn't bother dropping a day when a session ended on the same day as the next one began - but it's no big deal to see trends.
The sheet also breaks down whether Congress was in session during spring, summer, autumn, or winter. (But unfortunately not how many days.)
Anyway, a few patterns emerge:
- It oscillates between a low and a high number of days in session every other year from the get go (which I take it is related to partial elections).
- There are a few early peaks, related to wars, economic crashes, and pandemics.
- The Great Depression in particular has a lengthy period of high activity, as does WW2 and its aftermath.
- Things drop back to a lower (though still high) level of activity in the late 1950s, and the number of days in session has been trending up since.
- The oscillation is less dramatic after the 1950s, which I'd guess is due to air travel - allowing to campaign while still in session.
- The every other year oscillation almost completely disappears after the 2000-2001 crisis and 9/11 - possibly due to the internet allowing to campaign with less travel.
Side notes to follow up on the comment I posted:
- It was frequent at the beginning that sessions were so that you'd have summer off indeed (and sometimes spring). So your hypothesis about this being to have time to oversee a farm is likely, with the caveat that it was random enough that you could only realistically oversee a farm as a congressman, rather than work it yourself. :-)
- Farming-compatible seasonality seems to have begun to be less consistent beginning in the mid-19th century, presumably because of industrialization, and eventually disappeared entirely around WW2.
- When activity dropped back in the 1950s, it was autumn (
'[Sep 23-Dec 21(') that wasn't worked rather than the planting and harvesting months.
On that note, the two key periods you might be interested in in my opinion are:
- World War 1, the Great Depression, World War 2, during which the number of days in session springs up and then trends up from then onward. It's peak crisis, if you will.
- The mid-19th or so, corresponding to industrialization, where the sessions themselves no longer were as accommodating to farming as they used to be.