It is the most necessary substance for our life; it is the vehicle of
all odors and smells; it is the medium of all sounds, and brings to
our ear and so to our mind an immense knowledge of the outside world;
it is the cause of the beauty of the blue firmament or sky, of the
aurora and twilight; it is the great nurse of the whole vegetable
kingdom by clouds, rain, and dew.


What is an Aneroid Barometer?

It is a barometer in the construction of which no quicksilver or other
liquid is used. It consists of a metal box, exhausted of air, the top
of which is of thin metal, so elastic that it readily yields to
alterations in the pressure of the atmosphere. When the pressure
increases, the top is pressed inwards; when, on the contrary, it
decreases, the elasticity of the lid, aided by a spring, tends to move
it in the opposite direction. These motions are transmitted by
delicate levers to an index which moves on a scale. This barometer has
the advantage of being portable.


What is the Ear-trumpet?

A trumpet-like instrument used to aid deaf persons in hearing. Its
form is conical, and the larger end is of a bell shape; the small end
is placed in the ear, and the person talks in the large end. It acts
by concentrating the voice on the listener's ear.


What is a Stethoscope?