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The Scientific Scrapbook

Ionosphere Observatory


The lonosphere Observatory of the University, after a four-year shutdown, has resumed its radio investigations of the little-understood deep blankets of atomic particles which surround the earth's atmosphere a hundred or so miles from the ground, and which enable long-distance wireless communication.

After a year spent in preparing the Ionosphere Observatory equipment for reopening, the Harvard station is now making continuous automatic observations, 24 hours a day, of the heights of the ion layers vertically over Cambridge.

Within a few weeks this study will be supplemented by a program for continuous shortwave radio transmission and reception between the Harvard laboratories and a station at Rensselaer Polytechnic Institute, Troy, New York.

The radio studies over this long baseline will be carried out with automatic equipment set up within the laboratories, and with a specially equipped radio truck which will be used to make field observations between the two fixed stations.

The Harvard Ionosphere Observatory, located in the Cruft Memorial Laboratory, is under the direction of Harry R. Mimno, Associate Professor of Physics and Communication Engineering.

Scientists believe that continuous records of changes in the ionosphere will not only help to improve radio communication but may also yield vital information about the sun, about the nature of the upper atmosphere, and about earthly weather. Shifts in the ion layers occur constantly, and sometimes very rapidly, throughout the day and night, and are caused chiefly by changes in the intensity of the sun's radiation.

The Harvard Ionosphere Observatory is the only station in the United States now making continuous observations of the upper layers in a fixed frequency.

This work was first started in 1932. Harvard was forced to discontinue the research by the Federal communications Act of 1934, which prohibited the operation of any radio station without continuous attendances of an operator. The act was amended last spring to permit scientific research by automatic transmission, and the experimental program was set in motion again.

Phenomena found to affect the ionosphere are auroral displays, and terrestrial magnetic disturbances. An apparent close connection between radio wave propagation and weather conditions on the ground is being investigated by the Blue Hill Meteorological Observatory of Harvard, in cooperation with the radio engineers.

Observation of the ionized layers, which extend from about 30 to 150 miles above earth--well beyond man's reach-- is possible because the electric character of these blankets is such that they reflect radio waves back to earth. It is this reflection which makes it possible to send radio messages beyond the optical horizon, around the curve of the earth.

The characteristic which gives the ionosphere its name and usefulness to man is the fact that at his great height, where atmospheric pressure is almost at a vacuum stage, and the atmosphere receives the full intensity of the ultraviolet sunlight, atoms are readily ionized.

The atom, which is neutral in electric charge, becomes ionized when one or more of its tiny electrons is knocked away by an outside force. The particles resulting from ionization, including both the freed electrons and the remainder of the atom, have electric charges, and can exert electric force.

Solar radiation is the primary cause of ionization in this upper atmosphere, and changes in sun light caused by sunrise, sunset, sunspots, eclipses, or other phenomena, affect the blankets markedly. Harvard sent expeditions to New Hampshire in 1932 and to Russia in 1936 to study the effects of solar eclipse on the ionosphere.

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