I found this cool bulb in a dresser I bought at a thrift store. It appears the filament is continuous.  From what I could find, it was made between 1915 - 1920?  Are these rare? Can I screw it into a lamp to see if it works or would that break it? I was thinking I could put it on a dimmer with dimmer dialed down to not break the filament? Thanks!

That does look like an old one - neat find! Generally, it is a good idea to test old incandescent bulbs on a dimmer to reduce the thermal shock to the filament.

I have one a bit older than this but it made before 1920s
I think. This is a good piece to hang on to for sure.
A variac is the best. But a dimmer will do but dont run a dimmer to max as these vintage lamps rated 110 volts
As our line voltage is  near 120 volts, my line voltage can reach as high as 128 volts.

I have one that is very similar to this, if not the same. Mine still lights.