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The Telephone. -the Photophone

sometimes 90 per cent.) M. Mercadier has lately proposed a new plan, the essence of which lies in varying the source of light, making it flash up to its maximum at one moment, and reducing or extinguishing it at another. This can be done either by promptly varying a supply of oxygen to a low flame, or by varying the supply of combustible gas. M. Mercadier describes an ar rangement of the former kind, in which he uses a simple petroleum lamp of M. Duboscq; it has a round wick (which does not pass beyond the containing cylinder), and in the center rises a thin vertical tube, debouching a little below the plane of the wick. This tube admits the oxygen coming from a reservoir. The mode of admission is by pressure with the finger on a key, like that of a Morse apparatus; this has the effect of momentarily releasing a caoutchouc tube (by which the oxygen is conveyed) from the pressure of a clip. The flame then brightens. On taking the finger off, the supply of oxygen is stopped again, and the flame is reduced to very small size. This system, M. Mercadier says, has been adapted to apparatuses of optical telegraphy, and has given good results. He will shortly indicate how the same problem is solved with the electric light.

THE TELEPHONE ; OR, ARTICULATING TELEGRAPH.-In 1876 the first working instrument of this nature was introduced to the public. Its real merits were shown and fully proven before a large audience, by Prof. Graham Bell, in the Boston Music Hall, where communication was had with Providence, forty-five miles away. It is now (1881) in practical and successful operation over millions of miles, both in this and many foreign countries. The Bell telephone conveys plain articulate speech many hundred miles on telegraph wires. The British Government, which has for some years added the whole electric telegraph to their Post-Office system, have now added the Bell telephone to that organization. It is one of the most important and useful of human inventions.

THE PHOTOPHONE. --This remarkable invention is own sister to the telephone. It means, to talk by light. The idea upon which it is founded is this:

Certain substances are sensitive to light, and change their electrical condition according to the amount of light that falls upon them. To understand this, you may observe that colored cloths fade in the sun, and certain chemicals change their color in a beam of light, as in taking a photograph. This is called the actinic effect of light. This is a ne fact in nature, and upon it is founded the new apparatus for talking by light.

The apparatus consists, first, of a transmitter for causing the sound of the voice to affect a beam of sunlight. This is a thin diaphragm of silvered mica arranged somewhat like a diaphragm of a telephone. A powerful beam of sunlight is directed upon the