200 Reports on Special Researches 



on the pier-caps; these are operated by inilled heads on shafts projecting from the sides 

 of the pier, the mechanical details being built in with the brickwork. Suitable relief 

 springs are provided with each clamp to insure no damage to the tribrach bases of instru- 

 ments in case the clamp is set too far down. There are also 2 triangular piers, reaching 

 almost to the floor joists, in each of which are built for mounting tripods 3 brass pipe- 

 supports, each 3 feet long. The piers built above the floor will be used as mounts for 

 earth inductors, galvanometers, magnetometers, and special electromagnetic instruments. 

 The 3 piers in the baj^ are placed rather close together, to permit laying a stone slab across 

 them for testing magnetographs. 



The heating of the observatory will be by gas heaters of non-magnetic construction. 

 The illumination will be by alternating electric-current and semi-indirect 200- and 100- 

 watt lamps with floor outlets for special hand lights and connections. Special direct-current 

 circuits will also be installed for experimental work. 



In addition to the natural marks which are available for azimuth work, 3 piers with 

 engraved glass windows and electric lighting for night use will be placed at the extreme 

 north line of the property of the Department. 



The interior of the observatory is lined with wall-board, no plaster being used; this 

 gives a practically uniform insulation and will readily permit any future structural changes. 

 The joints in the wall-board are covered with cj^press battens to produce paneled effects 

 both on the ceiling and the walls. The large ceiling is relieved of monotony by five false 

 beams under the lower members of the trusses. 



As it is desirable, in an observatory of this kind, to have a fairly constant temperature 

 during the observational work, special provision was made against rapid changes of tem- 

 perature. Thus the walls consist of the outside siding laid over heavy building paper, 

 which in turn is placed on matched sheathing closely nailed on 2 by 5f-inch studding, on 

 the inside of which is placed with overlapping joints a layer of heavy building paper covered 

 by 1-inch battens, on which the wall-board, about ^\ inch thick, is nailed, thus providing 

 on all sides a 1-inch dead-air space. The floor of the building is double; the lower floor 

 is 1 by 6-inch matched pine closel}^ nailed, over which there is a layer of heavy building 

 paper; the finished floor is of edge grain J| by 2 inch Georgia pine. 



The construction of this building was undertaken by the Department, as it is difl^cult 

 to get satisfactory bids on structures built of non-magnetic materials. In consequence 

 the total cost was only $5,500, an average of about 14 cents per cubic foot of the total 

 volume. 



ACCESSORY STRUCTURES. 



There are at present on the site, besides the main building and the standardizing 

 magnetic observatory just described, two small non-magnetic huts which were formerly 

 used for intercomparisons of magnetic instruments. Thej- are now available for other 

 purposes, as, for example, atmospheric-electric observations. For the latter work, further- 

 more, an isolated wooden tower, about 80 feet high, is to be erected in 1915, on the top 

 of which a small hut for housing the atmospheric-electric instruments will be built. 



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