256 CARNEGIE INSTITUTION OF WASHINGTON. 



PHYSICAL LABORATORY. 

 INSTRUMENTS. 



The 500-k, w. direct-current generator set, mentioned in last year's 

 report, was delivered by the General Electric Company in March. 

 The set includes generator, synchronous motor, and exciter, the three 

 being direct-connected. The motor receives current at 2,200 volts, 

 the Southern California Edison Company supplying a special connec- 

 tion with its do\Mitown lines to provide for this additional load. The 

 generator is rated to supply 4,000 amperes at 125 volts, but the 

 adjustment of its field permits a range from 15 to 150 volts, a very 

 useful latitude for the service required in the laboratory. The three 

 machines are mounted on a common base which rests on a concrete pier , 

 all rigid connection wth the building being avoided. An alteration of 

 the laboratory building, involving the addition of a space 11| by 18 

 feet between this and the adjoining optical shop, together with all 

 work connected with the mounting of the generator set and its switch- 

 board, was taken care of by our Construction Division, while the elec- 

 trical work was done by the H. L. Miller Company. Massive copper 

 cables, aggregating 5,000,000 circular mils, are laid in ducts beneath 

 the floor from the generator to a convenient point in the laboratory. 

 The trials made of the installation, in various experiments since its 

 completion in June, have shown highly satisfactory operation in 

 every respect. 



The construction, beneath the floor of the optical shop, of a concrete- 

 lined tank of about 5,000 cubic feet capacity was completed during the 

 winter. Tests as to the use of water in cooling the solenoid magnet in- 

 dicated that difficulties from electrolysis would result. It was, there- 

 fore, deemed best to provide for cooling by kerosene, this to be cooled 

 in turn by the water in the tank. A system of pipes, forming vertical 

 grids, was built up in the central part of the tank and kerosene will be 

 circulated through these and to the apparatus by means of a pump. 



A trial solenoid, calculated to give a field of about 40,000 gausses, 

 with a tubular opening through the center, has been wound of bare cop- 

 per tape, the successive turns being insulated by cords, which provide 

 interstices through which the cooling kerosene may be forced. The 

 housing to contain the kerosene has also been made, but press of other 

 work in the machine shop during the summer has delayed the assembly 

 of the apparatus. 



Within the solenoid a tube electric-furnace in a vacuum-chamber will 

 be inserted. This will allow the examination of the Zeeman effect, 

 both direct and inverse, for those lines which are especially strong in 

 the furnace and often faint in other sources. High precision of meas- 

 m'ement may be expected to result from the intense field of the solenoid 

 in combination with the remarkably sharp lines produced by the 

 furnace when operated in vacuum at moderate temperatures. 



