Liquid Surface Is Flat
Bolivia salt flat
When a liquid fills up a container, regardless of the size, shape and orientation of the container, its surface is always flat. The surface is only curved when it is too small (less than one square inch) due to surface tension and it is called a meniscus.

Due to the flat surface, liquids will always flow to any lower point even at just 1 mm difference, towards finding their new level. Their own weight and its fluidity always make them seek their own level.

The long continuous reflection from the horizon to the seaside of sunlight during sunrise and sunset shows that the sea surface is flat. On Bolivia salt flat, the reflection from the whole sky can be seen on the flat water surface. Due to the flat water surface, a lighthouse can serve its function, in which it can be seen by ships far away. Submarine periscope can also function well with flat sea surface. Ships very far away from the viewer always appear upright to the viewer. Due to the characteristic of a liquid to seek its own level, spirit bubble levels can be used by builders to check whether something is truly horizontal. Builders fill a long transparent tube with a liquid and lay it across open land, sloping or not, to check that piles are level.

"Since any given body of water must have a level surface, no one part higher than another, and seeing that all our oceans are connected together, it follows that they are all virtually of the same level." - The English Mechanic, 26th June 1896

2016-11-13; 2016-11-21 by Ong Seng Aun.
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