Man's physical universe



teristic absorption pattern, which is identified by matching it with

patterns of known substances previously determined.

Ultrashort Radio Waves Have Many Applications.

Radio waves of less than ten meters in wave length are called ultrashort

radio waves. Previous to World War II they were used for a

two-way wireless telephone between France and England which

employed radio waves 18 cm. in length.

The shortest of these waves have been investigated only since 1928.

They were first produced by oscillating electric sparks, but later

vacuum tubes were used, because the waves produced by sparks are a

mixture of wave lengths. The smallest waves originally produced

with vacuum tubes were 30 cm. in length. When oscillations of sufficiently

high frequencies to produce shorter waves were generated,

the materials of the tube broke down because of the intensity of the

resulting electric fields. Later it was found that these frequencies

could be reinforced by proper tuning to produce much shorter waves.

Ultrashort waves can be focused and transmitted in the form of

narrow beams less than a square centimeter in cross section. This concentration

of energy presents the advantage that no energy is wasted.

An overwhelming proportion of the energy of longer radio waves is

wasted in space without being received. The ultrashort radio telephone

between France and England, mentioned above, requires an energy

output of only a fraction of a watt.

Short radio waves, about seven meters in length, with a frequency of

42,000,000 cycles per second, are now used to kill eggs, larvae, and

pupae of insects concealed in grain. Weevils, worms, mites, and other

infestations of cereals, cocoa beans, spices, tobacco, nuts, and similar

products are thus killed without injury to the products themselves.

It has been found that paresis, a disease due to syphilis, can be

cured by inducing malaria fever. In 1930 Whitney (1868- ) found

that a fever could be induced and controlled by short radio-wave

transmitters. Since that time many cases of paresis have been cured

by this method, although the old malaria method is still preferred by

some physicians.

Many remarkable experiments can be carried out

with powerful short-wave transmitters. For example, electric-light

globes can be made to glow several feet from the transmitter without

the use of any conductor. Popcorn can be popped in a cake of ice;

meat can be cooked in mid-air. So far the results obtained with such

transmitting devices have been more novel than valuable, but many

possibilities of practical applications are open.

Radiations of various kinds bring about profound changes in the

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