68 CARNEGIE INSTITUTION 



Buildings. 



The buildings for the observatory should be of the simplest con- 

 struction, designed for results, rather than for appearances. 



A. Spectroscopic ayid Bolornetric Laboratory. — Experience has shown 

 that in order to obtain good definition during the day the instru- 

 ments should be mounted at the greatest practicable height above 

 the ground. In the preliminary design for a separate spectroscopic 

 laboratory, the coelostat piers were accordingly carried up to a height 

 of 40 feet. A sketch was also made for a separate bolometric labo- 

 ratory. Subsequently, from motives of economy, a combination was 

 made of these two laboratories, wherein provision is made for one 

 16-inch and two 30-inch coelostats. The two large ccelostats would 

 be used for work requiring an image of the sun — one of them for 

 spectrobolometric observations, the other for work with the solar 

 spectroscope and spectroheliograph. The 16-inch ccelostat would be 

 employed for measurement of the solar constant. The spectroscopes 

 and spectroheliographs are mounted on piers so high as to be above 

 the level of the constant temperature house for bolometric work. 

 The piers may be constructed either of steel, ^properly ballasted, or 

 of granite, which is found in abundance near the summit of Mount 

 Wilson. The laboratory itself is of wood, supported on steel con- 

 struction, anchored to the rock. In the plans submitted provision 

 is made for mirrors of 200 feet focal length, but it is probable that 

 it would ultimately be desirable to extend the house 100 feet to the 

 north, thus permitting the use of a mirror of 300 feet focal length. 

 The construction of the building is such as to reduce to a minimum 

 the heating of the walls and the consequent currents of warm air. 



B. Reflector Dome. — For a reflecting telescope of 5-feet aperture, 

 mounted in accordance with the general plan shown in the draw- 

 ing,* a dome of 50 feet internal diameter is required. The walls of 

 the tower are built of thin she et iron, the track for the dome being 

 supported upon columns of steel construction. The sheet iron wall 

 is covered on the outer surface with wooden louvers in order to 

 prevent heating by the sun. South of the telescope pier is a con- 

 stant temperature laboratory, with piers for the concave grating^ 

 spectroscope. 



C. Office Building. — This includes offices and computing rooms 

 for all the members of the staff, together with shops for instrument 

 construction, library, laboratories, photographic rooms, etc., suitably 



* Not here reproduced. 



