Do you know some other properties of air?

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?

An instrument used by physicians for ascertaining the action of the lungs, judging by the sound of their motion whether they are healthy or not.

Describe the Audiphone.

It is a fan-shaped instrument to help deaf people, and is made of flexible carbonized rubber.  Fine silk cords attached to the upper edge bend it over, and are fastened by a wedge in a handle.  The top edge of this fan rests upon the upper teeth, and the sound waves strike its surface; the vibrations are thus conveyed by the teeth and the bones of the face to the acoustic nerve in the ear.

Describe the Telephone.

It is an instrument by which conversation may be carried on at a distance, and is composed of three parts—­a thin disk of soft metal, a small coil or bobbin of silk-covered copper wire, and a small bar magnet about four inches long.  The bobbin is placed on one pole of the magnet, so that the wire is as it were steeped in the magnetic space round the pole.  The metal disk is placed face close to the pole and bobbin, so that when it vibrates in front of the pole a series of wave currents will be set up in the coil of wire on the bobbin.  The whole is encased in wood, and a mouth-piece is provided for speaking against the disk.  The coil of wire on the bobbin is of course connected by its two ends into the circuit of a telegraph line.

Who invented the Telephone?

It was invented, almost simultaneously, by Alex.  Graham Bell, a native of Scotland, and Professor of Vocal Physiology in the Boston University, and Elisha Gray, of Chicago.