A collection of almost 16 Thomson Ammeters are arranged in rows and columns. These are used to measure the current in a circuit.

Thomson Ammeter Collection

Today I learned what an ammeter is. (Thanks Wikipedia!)

In the Rankine station control room, you'll find banks of switches, gauges, meters, etc. corresponding to the alternators in the Power House. This is where the station operators regulate the power and control the operation of the station.

This photo shows—among other things—the ammeters (Ampere Meters) which are used to measure the amount of current. This isn't the only thing measured.

I'm not going to pretend I understand the nuance (or even generalities), so I'll refer you to an excellent page by Professor Mark Csele:

A power station control panel is covered with meters, gauges and switches all arranged in columns (one column per alternator). A wooden desk with microphones is in front of the control panel. Archival photo from some time near 1910.
New control room: This archival photo was taken after the operating switchboard on the mezzanine level was moved into this new area. (This happened some time after 1910.) Each column of switches, meters and gauges corresponds to one of the 11 alternators in the Power House. The ammeters are the top rows in the image.