What caused the shift from calling things like rheostats and condensers to resistors and capacitors, or the move from cycles to Hertz?
It seemed to just pop up out of nowhere, seeing as the previous terms seemed fine, and are in use for some things today (like rheostat brakes, or condenser microphones).
I’m going to take a first stab at some parts of the question.
Regarding rheostat vs resistor, I don’t think one term replaces the other. In modern terminology, a rheostat refers to a two-lead device that varies in resistance. Whereas a resistor implies a fixed resistance. Rheostat brakes would make sense, since a fixed amount of braking current would be… unusual. “Variable resistance brakes” would mean the same, but is longer.
For cycles vs Hertz, I’ve not personally come across a technical reference which only listed “cycles”. Rather, old radios often list “cycles per second” when documenting the intermediate frequency, for example. So compared to writing “cycles per second” or “cps” over and over, Hertz is much shorter and easily abbreviates as Hz (eg MHz, kHz).
For condenser vs capacitor, I honestly haven’t any idea. I’m also keen to see some other answers to this question.