The pump, made by Christophe Bettally, is mounted on a wooden base and fitted with two brass barrels. Their pistons carry racks and are operated by a pinion fitted with two handles. A pair of small brass pillars supports the brass frame housing the mechanism. The glass bell-jar rests on a plate connected to the pistons. A stop-cock controls the flow of air between the pistons and the bell-jar. A mercury pressure-gauge or manometer was originally screwed onto the second stop-cock, inserted laterally into the connector between the plate and the barrels. The instrument is a French version of the English pump inv. 1536.