A nice one for the ruler collection. I've never come across one quite like this before, but I believe this sort of rounded handle ruler would have been used by a draftsman or architect, allowing for easy handling and movement across paper or blueprint. I have also seen a few round wood rulers described as writing rulers, and it does seem a good one for use in practicing calligraphy in ink, using the ruler and straight edge as guide then lifting/rolling it to avoid any smearing! 14 inches with inches marked in 1/8 inch increments. Looks maybe like copper to me, stamped what looks to me like C.E. Gibbs, Boston at center (which I've found no record of) and with a "patent applied for" mark near far left of the ruler. 

14 1/8" x 1 3/8" x 3/4" and in very good condition. It looks there may be a name carved into the wood but it is hard to discern.