This is a special little brooch. It came from a friend's estate. Her name was Ann. She died far too young and her husband gave this to me. We both loved thrifting and especially vintage costume jewelry
The pin measures 1.5" by 2.25 " and holds a functioning minature thermometer.
I often notice that early makers of vintage costume jewelry paid much attention to details, even on the back of pieces. The materials used in the creation of the jewelry may not have held much value but the workmanship did not reflect that.
I found one similar to it and it was given as a promotional trinket advertising Palmer Thermometers.