When Ivan is really ticked off by his mother's attitude, which favors Serebryakov over him, he complains and calls Serebryakov a "perpetuum mobile":
MARIYA VASILYEVNA: [to her son] You're just blaming your former beliefs for something… But they're not to blame, you are. You forget that beliefs alone are nothing, a dead letter… What you needed was action.
VOYNITSKY: Action? Not everyone can be a scribbling perpetuum mobile like your Herr Professor. (1.229-34)
Mariya doesn't really get what her son's trying to say, and readers might have trouble, too, if they don't know what a perpetuum mobile is. So let's break it down.
In Latin, perpetuum mobile literally means "perpetual motion," and the term is used to describe music that has lots and lots of notes continuing constantly, giving the illusion of lots of movement, like this.
It can also mean a piece of music that's meant to be repeated forever, in perpetual motion, like, say, "99 Bottles of Beer on the Wall." The idea is that Serebryakov is always busy as a bee, in constant motion, which delights Mariya and irritates Ivan.
Of course, this insult is ironic. Vanya and several others think that Serebryakov is kind of lazy, while Vanya and Sonya are the ones that work like crazy to keep the estate running. The thing is, their work isn't appreciated because it isn't the fancy intellectual stuff that Serebryakov does.
While we love a nice round of "99 Bottles," we have to admit that it's not exactly the most complicated, thoughtful piece of music out there. And that's why everybody's so upset by Vanya's use of the term. He's saying that Serebryakov seems busy and blustery, upsetting everyone in his path, but that he actually isn't going anywhere.
We also get the idea that maybe Serebryakov's work isn't all the interesting, after all. Maybe he's just spinning out the same old stuff all the time, or maybe his ideas only seem all hoity-toity intellectual but are really just a bunch of hot air. We don't know, because we never really find out what his ideas are. He certainly doesn't seem very thoughtful, right? Is it all just smoke-and-mirrors, perpetual motion going nowhere at all?