Capillary action of water in glass tubes. This shows water rising in a narrow glass tube, relative to a wider glass tube. For mercury sinking relative to the outside level of mercury, see image A350/168. The relative rise or fall of a liquid in a narrow glass tube depends on whether the liquid is attracted or repelled by the glass. Water has a positive capillary rise and is drawn up a narrow glass tube. Mercury has a negative capillary rise and sinks down a narrow glass tube, relative to the outside level.