I opened a 35 year old residential panel the other day and there was a device mounted to the inside wall of the box. It was a glass tube, about 1" diameter, 2-3" long. Brown material inside the glass with some information printed on the side but too worn to read. The leads at each end were connected across the 30 amp 240 volt dryer circuit. I haven't seen one before. I'm thinking surge protection. Anyone know what it might be?

Thanks.