ADVISORY COMMITTEE ON GEOPHYSICS 57 



contemplated work room, contains complete heat, gas, water and 

 electrical connections, and is thus potentially independent. 



16. Necessity for special powei- house . — The needs of the laboratory 

 in the matter of electric and other power will require careful con- 

 sideration before the final plans are prepared. Electricity for 

 charging storage batteries may be taken from any direct current 

 supply wires of proper voltage, i. e., preferably no or 120 volts. 

 Higher voltages involve special insulation and a great waste of 

 power, unless an unusual number of cells are arranged to be 

 charged simultaneously, which would be most inconvenient in a 

 laboratory of this character. Street car feeds are not suitable for 

 such a purpose ; the voltage is high (usually 500 volts) and 

 widely variable with the amount of traffic. Furthermore, if the 

 distance from the power house were large, no considerable supply 

 could be furnished to the laboratory without increasing the size of 

 the feeds — an item of unnecessarily large expense — or interfering 

 with the supply for the cars, a possible source of dissatisfaction, 

 both on the part of the railway company and the laboratory. 



Alternating current cannot be stored as such, and is, therefore, 

 best produced by special dynamos under the control of the institu- 

 tion ; the variations in a general supply main would be most disturb- 

 ing. An exception might be made in the case of very high poten- 

 tials, where the cost of a special wire from the power plant would 

 be small, and the current could then be controlled by suitable trans- 

 formers in the laboratory. 



It will certainly be more satisfactory and probably cheaper for 

 the institution to control its own electrical plant, especially as both 

 alternating and direct current is likely to be needed, and at varying 

 voltages, which would hardly be obtainable from outside. 



77, Summary cf Part II — The general requirements may now be 

 stimmed up as follows : 



I. A site, offering — 



(i) A rock foundation. 



(2) Permanent freedom from mechanical and electrical dis- 



turbance. 



(3) Sufficient elevation to insure dr>'uess and good light. 

 II. A two-story building with basement covering approximately 



12,000 feet of ground, and offering — 

 (i) A stable foundation for apparatus to which extreme 



stability is essential. 

 (2) A thoroughly insulated construction for controlling the 



temperature conditions within. 



