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Special Reports 



tion against sudden temperature changes inside the building. These considerations of 

 the requirements thus led to the adoption of a concrete, hollow-wall, monolithic con- 

 struction, using non-magnetic aggregates and non-magnetic brass reinforcement. 



Accordingly, a type of double-wall, concrete construction built by what is known 

 as the Van Guilder system was adopted for the Experiment Building. The machine used 

 in this system is a double mold, without either bottom or ends. In starting a wall the 

 machine is placed on the footing beginning at a corner, the two sides are filled and 

 tamped with concrete mixed to a stiff consistency such as will allow the immediate 

 release of the mold after filling, the mold then being pushed ahead ready for filling 

 and tamping on the next section. Each such operation completes a portion of the double 

 wall, approximately 9 inches high and 5 feet long. To get the strength and solidity of 

 the construction desired the two sections of the wall were made 6 inches thick, being 

 separated by a 2J^-inch air space. This system leaves the dead-air space continuous 

 except for the reinforcing rods tying the walls together. The operation of filling, tamp- 

 ing, and sliding the machine ahead is repeated until a complete circuit of the building is 

 made, when the next 9-inch tier is started. It is possible to cast the hollow wall rapidly 

 and to cast with one machine from 3 to 4 tiers per day. 



CENTER LIHB JOCEL Y N P L A C 1 



L1T1TI0II IN PUT 



Fio. 2. Plan of Grounds of Department of Terrestrial Magnetism, Washington, D. C. 

 A. Main laboratory. B. Standardizing Magnetic Observatory. 



C and D. Accessory buildings. E. Experiment Building. 



F. Foundry, storehouse, and stable. 



