94 CARNEGIE INSTITUTION OF WASHINGTON. 



Solar Observatory, flount Wilson, Cal., Dr. George E. Hale, 

 Director. Grants Nos. 70 and 185. $15,000. 



As the result of the favorable report made by Professor Hussey 

 in 1903, a careful test of the conditions for solar work on Mount 

 Wilson (altitude, 5,886 feet) was undertaken by Dr. Hale in the 

 winter of 1 903-1 904. In March, 1904, the work of erecting on the 

 mountain a 15-inch coelostat telescope of 61.5 feet focal length was 

 undertaken. The instrument was ready for use early in April, and 

 some excellent photographs of the sun were obtained with it. Since 

 that time a I^ittrow spectroscope of 18 feet focal length has been 

 employed with the telescope in a study of the spectrum of the 

 fiocculi ; the resulting photographs are much superior to those pre- 

 viously obtained, and throw new light on the nature of the fiocculi. 



With the aid of meteorological instruments furnished by the 

 Carnegie Institution, daily observations of the temperature, wind 

 movement, and humidity were commenced in April and have been 

 continued regularly ever since. These indicate remarkably favor- 

 able conditions for astronomical work because of the great amount 

 of clear weather and the low humidity and wind movement. Up to 

 September i, 132 days out of 136 were suitable for observations. 

 Daily observations of the sun have been made with a small telescope 

 throughout this period. These show that the definition is superior 

 to that of any other site with which Dr. Hale is acquainted. A 

 complete report on these observations has been prepared and will be 

 submitted to the Carnegie Institution. 



In April, 1904, the Carnegie Institution made a grant to provide 

 for the erection and use on Mount Wilson of the Snow coelostat 

 telescope of the Yerkes Observatory. Since that time the work of 

 construction on the mountain has been pushed forward as rapidly 

 as possible, and it is hoped that the instrument may be ready for 

 use before the end of the present year. In order to transport the 

 heavy parts of the instrument to the summit of the mountain it was 

 necessary to widen and improve the narrow trail, over 9 miles in 

 length, which leads to the valley. A special carriage was also con- 

 structed for this work, and at the present time this is making the 

 round trip daily. Practically all of the heavy parts of the instru- 

 ment, including the mirrors, are now at the summit of the moun- 

 tain. The large stone piers required for the coelostat and the solar 

 spectroscopes have been completed, and the house which is to cover 

 the instrument is being erected. A small machine shop, with gaso- 

 line engine and djmamo, has been constructed on the mountain to 



