provisional site, and $10,000 was appropriated for a thorough trial of the mountain. Later the institution decided to undertake the construction and equipment of a solar observatory at this point and up to the present time has devoted more than $300,000 for the purpose. Professor George E. Hale, former director of the Yerkes Observatory, has been made permanent director, and under his care the installation of the observatory has gone forward with characteristic energy. At the present time the Snow horizontal telescope and various buildings necessary for the proper execution of the work of such an observatory are Hearing completion. The program of work which Professor Hale has laid out, in a very condensed form, is as follows:
| The ends sought are two: | |
| (1) The Study of the Sun as a Typical Star. | |
| (2) The Study of the Sun as the Center of the Solar System. | |
| The investigations include: | |
| I. Direct photography. | |
| (a) Daily photographs of the Sun on a Scale of 6.7 inches. | |
| (b) Large scale photographs of spots and other regions. | |
| II. Photographic Studies of the Solar Atmosphere with the Spectroheliograph. | |
| (a) Daily photographs of the Sun taken with H1, H2, and Hδ, and other dark lines for calcium flocculi and prominences. | |
| (b) Measurement and discussion of the photographs. | |
| III. Spectroscopic Investigations. | |
| (a) Daily photographs of spectra of spots. | |
| (b) A study of velocity of motion of flocculi and prominences. | |
| (c) Bolometric measurements of relative radiation of sun-spots, faculæ, and photosphere. | |
| (d) Spectroscopic measurement of solar rotation. | |
| IV. Studies of total solar radiation. | |
| V. Comparative laboratory investigations. | |
The Snow horizontal telescope is provided with two concave mirrors, one of 60 feet focus, and the other of 145 feet focus, either of which can be used as desired. The beam of sunlight falls first upon a plane mirror of 30 inches diameter, whence it is reflected to a second plane mirror of 24 inches diameter, which sends it to the concave mirror of the telescope. With the image thus obtained any of the pieces of work outlined above may be carried out.
The spectroheliograph is the creation, in large part, of Professor Hale himself, in whose hands it has led to remarkable results. The principles involved seem to have been suggested first
