Page:Popular Science Monthly Volume 91.djvu/761

This page needs to be proofread.

Popular Science Monthly Making Telephones and Pho- nographs Speak Perfectly

A TELEPHONE receiver for reproducing the sounds of the talking voice without any of the hissing, spitting and scratch- ing that now accompany tele- phone conversation, is an in- vention of Erik Christian Bayer, of Denmark.

This receiver works on an en- tirely new principle. Instead of a single sound-producing dia- phragm, his device uses a num- ber of wires. These wires vary in length much like those of a piano, and each wire produces its own fundamental tone. And like the wires of a piano, they vibrate with different strengths and thus produce other complex sounds. In this way, the reproduction of voices is obtained. By eliminating those wires which would produce the sing- ing and other noises in the telephone line, these foreign sounds are entirely excluded from the transmission.

By connecting the ordinary phonograph, through a telephone transmitter, with this novel receiver, Bayer hopes to strain out all impure secondary sounds — even the scratching of the needle itself.

This application of the idea although simple, does not seem practical, however; for it is only reasonable to infer that the impure sounds that might possibly be in- troduced by the transmitter would be almost if not equally as annoying as those weeded out. The photographs below show


��� ���The form is moved along from section to section of the wall. There is no waiting for the concrete to set. It is possible to erect three or four ten-inch courses during a day


��the diagram and application of the device.

��Source of direct current

���Any Boy Can Build a Concrete Wall with This New Metal Form

WISCONSIN man has invented a new type of metal concrete form for constructing hollow or solid concrete walls. The supporting frames of the form are rigid while the arms supporting the mold boards are of flexible spring steel which prevent the form from bending out of shape. The rigidity of the form makes it possible to erect walls true and straight. Fresh concrete is spread into the mold and tamped down until the mold is com- pletely filled. Then a lever is raised which releases the machine from the wall. The form is moved along and another section of the wall is formed. There is no waiting for the concrete to set. It is possible to erect three or four ten- inch courses in a day.

The expense and waste of lumber in building forms is done away with. Bytheaid of this form any novice can erect cement walls for buildings or partitions.

��The electric current going through the wires, vibrates them and produces the voice sounds. All wires that would set up other sound vibrations are inactive

�� �