Those who have not already tried the experiment may be interested to know that a telephone may be made to sing by holding the receiver about 1/16 in. from the transmitter, as shown in the illustration. The experiment will work well on most telephones, but not on all.
When the receiver is placed in the position shown it acts like an ordinary buzzer, and the function of the transmitter will then be that of an interrupter. The slightest movement of the transmitter diaphragm will cause an increased movement of the receiver diaphragm. This in turn will act on the transmitter, thus setting up sympathetic vibrations between the two, which accounts for the sound.
A Microscope Without a Lens
By E. W. Davis
Detail of Lensless Microscope
Nearly everyone has heard of the pin-hole camera, but the fact that the same principle can be used to make a microscope, having a magnifying power of 8 diameters (64 times) will perhaps be new to some readers.
To make this lensless microscope, procure a wooden spool, A (a short spool, say 1/2 or 3/4 in. long, produces a higher magnifying power), and enlarge the bore a little at one end. Then blacken the inside with india ink and allow to dry. From a piece of thin transparent celluloid or mica, cut out a small disk, B, and fasten to the end having the enlarged bore, by means of brads. On the other end glue a piece of thin black cardboard, C, and at the center, D, make a small hole with the point of a fine needle. It is very important that the hole D should be very small, otherwise the image will be blurred.
To use this microscope, place a small object on the transparent disk, which may be moistened to make the object adhere, and look through the hole D. It is necessary to have a strong light to get good results and, as in all microscopes of any power, the object should be of a transparent nature.