long range barometer

A barometer, the upper portion of whose tube is in spiral form, and of diminished diameter, the distance between the coils being usually 12 base to 1 perpendicular, so glycerine. The rising and falling of the mercurial column in the large tube, having a lighter fluid to balance, and that dispersed over a larger space by reason of the difference in the diameter of the two tubes, a longer range is obtained, due both to the unequal capacity of the two tubes and the difference in the specific gravity of the two fluids. These barometers admit of minute variations being read without the aid of a vernier.