Picked up this nice working thermo "Canada Neon-Ray Co. MADE IN USA"

Is there an easy method to open these up to clean the glass lense? There appears to be a very fine seam but not sure if I'm just seeing things or not. If there is no easy or safe way to open, then it will stay the way it is.

GM Delco round Thermometer-1.jpg
Terry Tramp

I'm interested in Deep Rock and Kerr McGee items especially if they are marked B.A. Tramp Oil