In 1916, when the following text was written for Dodd, Mead and Company's New International Encyclopedia, physicists were convinced that light propagated like sound through the medium of ether, and that Mars was not only covered with canals but enveloped in an atmosphere similar to our own.

Nearly a century later, this Red Planet lives on only as a ghost, haunting the imagination of children and the scientifically unschooled.

Beginning with the telescopic researches by Sir William Herschel, Mars has possessed special interest owing to the indication of the existence upon its surface of physical conditions not unlike those of the earth.

Many things seem to indicate that Mars is enveloped in an atmosphere with physical properties similar to those of the earth's atmosphere.

According to observations by Lowell at Flagstaff, Arizona, carried on for six months, this atmosphere would appear to be of remarkable clearness.

Two white patches, in the neighborhood of the poles, are very conspicuous and so brilliant that they, in the proper light of the sun, have been seen sparkling like stars. They are generally explained as accumulations of snow and ice, and this view is supported by the fact that they change with the Martian seasons.

A mixture of orange patches and gray-green markings is seen extending over more than half the surface of the planet in a central zone, almost parallel to the equator.

The orange patches are assumed to be land. This assumption is based on the similar appearance that the great deserts of the earth would present under the same conditions. Also permanent markings on these patches have been observed.

The gray-green markings were at first explained to be seas and Sir William Huggins discovered water in the atmosphere of Mars, but the observations of Douglas in Arizona (1894) and Barnard at the Lick Observatory (1896) seem to disprove the aqueous character of these "seas."

In 1894 Lowell and Pickering discovered, a month after the Martian vernal equinox, a dark belt connected with the south polar cap, which was explained by them as a gathering of water resulting from the melting of the cap by the summer heat. A similar appearance has been observed around the north polar cap.

Of all the markings that have been observed on the surface of Mars the "canals" have created the most interest.

Since their first observation at the very favorable opposition of the planet in 1877 they have been studied carefully at later favorable oppositions.

They have been described by observers as faint lines, becoming finer and straighter at closer observation, following the course of great circles, and distributed like a network over the surface of the planet. Several appear to pass through the same point, at which round spots, called lakes, are seen.

Various theories have been advanced for the explanation of this "canal system." They were first taken to be waterways, and the change in their appearance was explained as due to the Martian seasons. Pickering considered them to be tracts of land rather than waterways.

Lowell advanced the view that these "canals" and "lakes" constituted a system of irrigation carried out by the inhabitants of Mars for the purpose of leading the water obtained from the melting snow of the polar regions over the surface of the planet.

It has been urged that the appearance of the canal system may be nothing but an optical illusion, but Lowell in 1905 obtained photographs which seem to settle decisively the question of the reality of the canals.