|Fridtjof Nansen, Shale Niskin oceanography|
Fridtjof Nansen had to wonder whether the seawater was layered— how temperature and salinity varied with depth. He had to wonder and to figure how to get the data. The famous explorer and statesman Fridtjof Nansen combined a reversing thermometer with a bottle, both being triggered by a “messenger weight” to capture temperature and a water sample at a given depth.
The Niskin bottle doesn’t need to be rotated to trap a water sample, and is made of plastic to reduce contaminating its sample. Some Niskin bottles are preset to close at a given depth and some are triggered by an electric signal from the surface. Many Niskin bottles may be mounted on a rosette to capture temperatures and samples at many depths.
You had to wonder and the point is people didn’t, which is why one rarely needs to prove it isn’t obvious.