280 CARNEGIE INSTITUTION OF WASHINGTON. 



New work. — The principal new work may be summarized as follows: 

 (1) Completion of three standardized atmospheric-electric conductivity- 

 apparatuses for the photographic registration of both positive and negative 

 conductivity after the designs developed last year, for use at the Department's 

 observatories; (2) the design, preparation of drawings, and partial construc- 

 tion of three standardized potential-gradient apparatuses with photographic 

 registers for observatory use; (3) partial construction of two standardized 

 photographic registers for atmospheric-electric instruments for experimental 

 and emergency use; (4) construction of six field galvanometers and tripods as 

 developed and designed by the Department for use with earth inductors (these 

 are Department Nos. 31X to 36X); (5) design, preparation of drawings, and 

 partial construction of ten standardized string electrometers somewhat along 

 the lines of the Wulf type. Other new work included a special compass 

 attachment for dip circle designed and constructed for use during sledge-trips 

 on Captain Amundsen's Maud Expedition ; with this design sightings may be 

 made directly on celestial bodies, so that, together with the sextant and artificial 

 horizon for time-work, the dip circle may serve for the complete determina- 

 tion of the three magnetic elements. Besides other special equipment for the 

 Maud Expedition, a potential-gradient apparatus for absolute observations 

 was designed and constructed with necessary accessory equipment and reserve 

 parts. 



Experimental work. — Considerable time was given to the accurate finishing 

 of eight rotors and to the finishing and aligning of shaft connections between 

 rotors and motor-drive for Dr. Barnett's special investigations on magnetiza- 

 tion by rotation. About 100 pounds of non-magnetic brass and "lumen" 

 castings were also made for the Section of Experimental Work in Magnetism, 

 and other miscellaneous assistance was given from time to time. A special 

 experimental apparatus for the investigations by Mr. Peters regarding in- 

 strumental dynamic deviations on board ship was constructed, as also mis- 

 cellaneous appliances for other experimental work. 



Improvements and repairs of instruments. — All instrumental equipments for 

 the field parties dispatched during the year were thoroughly overhauled, 

 repaired, and readjusted as necessary. Because of the lack of a sufficient 

 number of earth inductors for field use, special arrangements were made to 

 adapt marine earth-inductors Nos. 3 and 7 for land observations. A telescope 

 mounting was provided for earth inductor No. 3, so that this instrument might 

 be used for rapid determinations of declination as well as of inclination. 



Miscellaneous. — Seven general drawings and detail drawings were com- 

 pleted of the Department's design of magnetometer-inductor. 



The drawings for standardized atmospheric-electric equipment and for the 

 various observatory buildings were kept current according to the instrumental 

 and constructional developments. 



A motor-pit with concrete walls and housing was built on the east side of 

 the Experiment Building, and a number of concrete piers and changes in 

 piers and motor-pit as necessitated by the development of the experimental 

 work on magnetization by rotation were made. A substantial reinforced- 

 concrete pier for mounting of special collimating mark for the standardizing 

 magnetic observatory was placed at a point about 280 feet north of the obser- 

 vatory, and the necessary mechanical work for mounting the collimating lens 

 and its reticle was begun; the general plan for this work was developed by 

 Mr. Johnston. 



