Early Coal Conversion Thermostatic Control???

My family and I recently visited the Conrad-Caldwell house museum in Louisville, Kentucky’s historic district and I came across this curios device and plaque hanging in the back servants stair hall and was looking for any information I could come up with for it. Please read the plaque as the museum docents really are not sure about it either. There is wire coming from the backside of it but couldn’t tell it it really was connected to it. The boiler was originally coal fired but had been later converted or even completely replaced by gas fired I’m guessing. The house was built in 1893-1895. The Caldwells were very wealthy and had the latest when the hose was built including electric-combination lighting. So, any ideas about this curious device? Thank you.