Bottle Coasters. Coasters were in popular use by the 1750s. They were invented to enable guests to slide decanters or wine bottles across the table without scratching the surface. They also served to catch drips which might stain the table. Coasters had baize-covered or polished wooden bases (like this one), and later versions sometimes had wheels.
Gentlemen could not drink freely, or at least as much as they wished, until the end of the meal when the ladies had withdrawn to take tea or coffee in the drawing room. The butler laid out the appropriate glasses in front of each guest. He placed the decanters, on coasters, before the master of the house to be passed around in an informal and relaxed atmosphere. Reference: Victoria and Albert Museum