CONSTRUCTION OF NON-MAGNETIC EXPERIMENT BUILDING OF 

 THE DEPARTMENT OF TERRESTRIAL MAGNETISM. 



By J. A. Fleming. 



Preliminary experiments pertaining to fundamental problems in magnetism, made 

 during 1918 in the main laboratory of the Department of Terrestrial Magnetism at 

 Washington, D. C, showed the desirability of erecting on the Department's site, a 

 non-magnetic building of special design, designated the "Experiment Building." For 

 this purpose the Trustees of the Carnegie Institution of Washington made a special 

 allotment of $10,000 to cover costs of construction of the proposed structure, inclusive 

 of heating arrangements, electric circuits, laboratory tables, and other internal furnish- 

 ings. The plans were prepared by the author, in conference with Dr. S. J. Barnett as 

 to the various requirements, and in accordance with the Director's instructions. Effec- 

 tive assistance in the preparation of the plans was received from Mr. C. Huff, a member 

 of the Department's construction and instrument staff. 



The main requirements were: (a) a site sufficiently removed from the main lab- 

 oratory to assure that the effects caused by the large amount of magnetic material and 

 apparatus in that building would not seriously affect the desired uniformity of magnetic 

 field inside the Experiment Building; (6) unusual rigidity and stability; (c) essentially 

 non-magnetic construction in order to secure the required uniformity of magnetic field 

 within the building; (d) provision against rapid temperature changes within the 

 building in order to maintain such constancy of temperature as the experiments may 

 require; and (e) style of architecture to be in general harmony with that of the Stand- 

 ardizing Magnetic Observatory 1 already on the grounds. 



After careful consideration of suitable locations available for building purposes 

 within the grounds of the Department, and after some tests had been made, a site (E), 

 about 200 feet north of the main laboratory (A), was selected as shown in Figure 2. 

 The site chosen made possible the economical utilization of the facilities and sources of 

 supply of the laboratory (A) and of its extensive heating and electric equipment. It 

 was not practicable to use the Standardizing Magnetic Observatory (see B, Fig. 2) 

 for the experimental work in magnetism, since that building is constantly in use as a 

 non-magnetic observatory for standardizations and intercomparisons of instruments, and 

 for special observations. 



Since the publication of Volume II, the site of the Department as shown in Figure 1 

 on page 187 of that volume has been increased by the addition of parcels to the north 

 and at the southeast corner, while a part of the original site on the eastern side of the 

 property has been disposed of by exchange. Accordingly, the total area of the Depart- 

 ment site is now increased from 7.4 acres to about 8.8 acres; it is inclosed on the south 

 and west by established highways and extends on the other boundaries, either to the 

 center fines of proposed streets, or to the edges of streets actually in construction. 



The construction of the Experiment Building could be begun in April 1919. Because 

 of the scarcity of skilled labor and of most building materials in 1919, it was decided to 

 use concrete as the main material of construction, selecting a cement which was so nearly 

 non-magnetic that its distribution in the walls of the building would have practically 

 no disturbing effect upon the uniformity of the magnetic field within the area of the 

 experimental work. It also appeared that a double wall, thus providing a dead-air 

 space, would offer the most feasible and economical arrangement for the desired protec- 



1 See Researches Dep. Terr. Mag., vol. II, pp. 185-200, 1815. 

 351 



