The the weight of the atmosphere

1365. With respect to the changes in the weight of the atmosphere, it is generally known that the instrument called the barometer shows the weight of a body of air immediately above it, extending to the extreme boundary of the atmosphere, and the base of which is equal to that of the mercury contained within it. As the level of the sea is the lowest point of observation, the column of air over a barometer placed at that level is the longest that can be obtained.