or Manoscope, an instrument to show or measure the alterations in the rarity or density of the air. The manometer differs from the barometer in this, that the latter only serves to measure the weight of the atmosphere, or of the column of air over it; whereas the former serves to measure the density of the air in which it is found, and this density depends not only on the weight of the atmosphere, but also on the action of heat and cold, and other circumstances.