This lamp has a clear glass ribbed or "reeded" font, a brass stem and marble base.
Probably by Atterbury Co. of Pittsburgh, ca. 1870 (similar shown in Thuro)
Size: Approximately 8.5" high, base 3.5" square.
Condition: Good. Some slight denting/marks to brass. No chips, cracks or repairs.
Note that I try to be conservative about condition descriptions, carefully noting any flaws. Of course, with antique items, there will be some signs of usage, and/or manufacturing defects. But overall, my customers have always been pleasantly surprised upon receiving their items, and of course, returns are no problem if I happen to miss anything.