From Glossary of Meteorology
A device used by oceanographers to obtain subsurface samples of seawater.
The "bottle" is lowered by wire with its valves open at both ends. It is then closed in situ by allowing a weight (called a messenger) to slide down the wire and strike the reversing mechanism. This causes the bottle to turn upside down, closing the valves and reversing the reversing thermometers, which are mounted on the bottle in a special thermometer case. If, as is usually the case, a series of bottles are lowered, then the reversal of each bottle releases another messenger to actuate the bottle beneath it.