4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



The galvanometer was of the D'Arsonval type furnished with the 

 Angstrom pyrheliometer and pyrgeometer. It also was modified, 

 first, hy adding a lever device giving means for setting the scale zero 

 as desired ; second, by removing the iron damping core, thus insuring 

 a definite first swing under all conditions of use. All the pyrano- 

 meter measurements were made according to the first-swing method 

 described in detail in the paper " On the Use of the Pyranometer " 

 (Smithsonian Misc. Coll., Vol. 66, No. n). 



Weston Milliammeter No. 8,244, reading to 1.5 amperes and pre- 

 viously calibrated at the Bureau of Standards, was used. 



As a measure of precaution a duplicate pyranometer, galvano- 

 meter, and ammeter were brought from Washington, but by good 

 fortune were not needed. 



The pyranometer was mounted outside on a pier about 6 meters 

 west of the shelter which enclosed all the auxiliary apparatus and 

 at an altitude of 1.5 meters above the ground. The absorbing strip 

 was horizontal and was exposed to almost a complete hemisphere of 

 sky, only a small portion of the sky low in the east being cut off by 

 the barn. Inside the barn, the galvanometer was hung on a solid 

 wooden pier, well protected from wind or temperature changes. In 

 front of the galvanometer another pier supported the ammeter, rheo- 

 stats, and dry cells which furnished the calibrating current, and a 

 dial resistance box. This box was inserted in the galvanometer 

 circuit, enabling the observer at the galvanometer to keep the deflec- 

 tion always of suitable magnitude. 



For the photographic work, a portion of the west wall and roof 

 of the barn sufficient to expose the lenses to the sun during the dura- 

 tion of the eclipse was removed and the remainder of the barn was 

 made a better protection by covering cracks with strips of batting. 

 Two tubes of 8 inch (20 cm.) iron stove-pipe, riveted together in 

 lengths 11 feet (335 cm.) long, formed the tubes for the double- 

 barreled camera. These were mounted on a polar axis which itself 

 was supported by two wooden posts embedded in cement and well 

 braced. An arm 8 feet (2.5 meters) long, clamped to the polar axis, 

 extended due west and moved downward over a roller, thus causing 

 the camera tubes to follow the apparent solar motion. The rate of 

 motion was regulated by a clockwork placed on a pier just above the 

 end of the lever arm. 



The photographic plates used were 8 by 10 inches (20 x 25 centi- 

 meters) Special Red Label brand, made by the Hammer Dry 

 Plate Co. 



