Phonograph records are now made with one hundred grooves to an inch. Each groove is not more than four one-thousandths of an inch deep. A lever tipped with sapphire cuts the grooves. Its tiny marks have been photographed—one way of seeing a sound!
What the phonograph does
The phonograph is used everywhere for amusement. It preserves the voices of great singers for the future. With it songs and bits of folklore can be collected in languages that are now dying out.
The electric light
Edison has put into practical use many principles discovered by other men. He does not claim to be the discoverer of the electric light. He did much, however, to make it useful to people in lighting their houses, and also in lighting great cities.
The first great electrical exhibition
In the winter of 1880, in Menlo Park, Edison gave to the public an exhibition of his electric light. Visitors came from all parts of the country to see this wonderful show. Seven hundred lights were put up in the streets, and inside the buildings. Edison had produced a much better light than any that had been used before.
202. A Great New Industry. Edison also had a part in another invention for which Americans can claim most of the credit—moving pictures.
Settling a racetrack dispute
A dispute about horseracing did most for the discovery of moving pictures. The question was whether a horse ever had all four feet off the ground at once. To settle it, Edward Muybridge, an employee of the government, was called in. He stretched cords, fastened to the shutters of a row of cameras, across a racetrack. As the horse ran past, it took its own pictures. Later Muybridge made a camera which would take pictures very quickly, but he could not show his pictures well.