Page:Popular Science Monthly Volume 86.djvu/221

The wise economical policy of this observatory is to engage principally in those investigations which can not be carried on with smaller and less effective instruments. Much that could be done there is left to smaller institutions. The great instruments are used only for the problems that demand their great power. And these are quite sufficient to keep them in constant use.

Turning now to the Mount Wilson Solar Observatory we find a unique institution. As its name implies, it is an observatory erected primarily for the study of the sun.

In 1902, Dr. S. P. Langley addressed a communication to the Carnegie Institution recommending the establishment of an observatory at a very high altitude for the special purpose of measuring the solar radiation.

This recommendation resulted ultimately in the erection of the Solar Observatory by the Carnegie Institution by which it is supported. Various sites in Arizona and in southern California were tested, and the summit of Mount Wilson (nearly 6,000 feet above sea-level) near Pasadena in southern California was selected. In the choice of a site for this observatory excellent "seeing" conditions in day time as well as at night were of primary importance. Such conditions were found to exist on Mount Wilson.

For director of the observatory a very wise choice was made in Dr. George E. Hale. It is due principally to his genius and untiring efforts that this wonderful plant has been designed and brought to its present high state.

Dr. Hale points out that the term "solar observatory" is to be used in a broad sense,

since it is not intended to exclude from the program certain investigations of stars which are of fundamental importance in any general study of the problem of stellar evolution. For the sun is a star, comparable in almost every respect with many other stars in the heavens, and rendering possible, through an intimate knowledge of its own phenomena, the solution of some of the most puzzling questions in the general problem of stellar evolution. Conversely, however, the stars are suns, and if we would know the past and future conditions of the sun, we must examine into the physical condition of stars which represent earlier and later stages of development. It will be seen that there is ample ground for the inclusion in the equipment of a solar observatory of certain instruments especially designed for the study of stellar problems.

Such an observatory, whose primary object is "to apply new instruments and methods of research in a study of the physical elements of the problem of stellar evolution," must of necessity have as complementary parts of its equipment a physical laboratory and an adequate machine shop. These two parts have been supplied and are located in Pasadena. Here not only are smaller pieces of apparatus made and repaired, but also the enormous discs of glass for the 60-inch and the 100-inch reflectors have been figured and tested.

The instrumental equipment of the solar observatory is naturally