I'm having difficulty reproducing an experiment I remember from high school. It's basically a glass bottle with a rubber stopper through which runs a glass tube, bent to form a horizontal portion. A drop of water sits in the horizontal portion. When the external air pressure changes, the air in the bottle expands or compresses as indicated by movement of the drop. I remember the whole class trooping up the stairs with our physics teacher, from basement to top floor, and the drop clearly moved. I have a 1.5 liter bottle with a 2-hole stopper. One hole has a straight piece of 2 mm tubing extending a few cm above the stopper. The tubing in the other hole is bent into a 3/4-turn spiral leading to a horizontal section of about10 cm. (The curl is a trap to make it less likely that the drop will fall into the bottle.) After the drop is positioned properly, the vertical tube is plugged with a bit of caulk. Initially, I had trouble with the drop shrinking and tending to move toward the bottle. I theorized it might be evaporating into the bottle, and keeping a little water on the bottom of the bottle seemed to fix that. Experiments 1. Warming the bottle with my hands produces a gratifying motion of the drop away from the bottle, proving that any leaks are not too bad. 2. Changing elevation produces no discernible motion, although the calculated motion for 8 ft of elevation is 14 cm! 3. Tilting the assembly so that the 'horizontal' tubing is vertical makes the drop move about 2.5 cm, while the calculated motion is ~ 10 cm! I also observe that the drop moves very slowly, suggesting high friction force against the glass. The menisci are very pronounced, suggesting that capillary forces have a major effect. But I don't see how that can destroy the barometer function. Calculations Air pressure gradient at sea level is 0.012 %/m. 8 ft = 2.44 m = 0.029 %. 0.029 % of 1.5 liter = 0.44 ml = 440 cu mm. Cross section of 2 mm bore = 3.14 mm Predicted displacement = 440/3.14 = 141 mm ~ 14 cm. Pressure exerted by a 10 m column of water ~ 1 Atm. Pressure exerted by a 2 mm long drop = 0.0002 Atm = 0.02 % That should cause a displacement of 9.7 cm.