The two-fluid barometer, invented by Descartes and constructed by Huygens, has been undeservedly neglected. It combines almost the compactness of the mercury barometer with almost the sensitiveness of the water barometer. Two patterns, the straight-tube and the J-tube, are described in this paper. Reasons for preferring the J-tube pattern are given. Neither pattern requires more than routine glassblowing skill. The two fluids may be mercury and butyl phthalate. Instructions for filling the barometer are included. The finished instrument is a good teaching piece and is interesting to the general public, but it is not recommended as a replacement for the standard mercury barometer when highly accurate readings are needed.