946 



SCIENCE. 



[N. S. Vol. XIX. No. 49.5. 



higher frequency machine may be used 

 alone. Transformers are arranged to 

 change these two-phase currents to three- 

 phase when desired. 



5. Another three-machine set is under 

 construction by the General Electric Co. 

 This contains two 60-cycle three-phase 

 alternators, with adjustable phase relation 

 and surface windings, giving nearly sine 

 wave form. 



Special attention has been given to the 

 matter of accurately measuring frequency, 

 phase and wave form as well as alternating 

 voltages, currents and power. These latter 

 quantities are measured by means of in- 

 struments which admit of accurate calibra- 

 tion with direct currents and electromotive 

 forces, the latter being measured by po- 

 tentiometers, using standard resistances 

 and Weston cells, the e.m.f. of the latter 

 being of course known in terms of the 

 standard Clark cells of the bureau. Thus 

 all current, voltage and power measure- 

 ments, both direct and alternating, are re- 

 ferred to standard resistances and standard 

 cells. 



The alternating instruments employed 

 are as free as possible from errors due to 

 inductance, eddy currents and capacity. 

 Corrections are applied for the effects of 

 small residual inductances when necessary. 

 The alternating generators employed are 

 driven by motors operated from storage 

 batteries, enabling the speed and voltage 

 to be maintained very uniform and meas- 

 urements to be made with great precision. 

 Thus frequency, voltage, power factor and 

 wave form are controlled and varied as 

 desired, and every effort is made to secure 

 accurate measurements. 



The bureau is now prepared to test alter- 

 nating voltmeters, ammeters or dynamom- 

 eters, wattmeters, watthour meters, phase 

 and power factor meters, frequency indi- 

 cators and other similar apparatus. Re- 

 cently some very careful tests have been 



made on a lot of watthour meters to deter- 

 mine separately the effects of varying the 

 voltage, frequency, power factor, tempera- 

 ture and wave form from the normal con- 

 ditions, and of the load from 1 per cent, 

 to 150 per cent, of normal full load, and 

 curves plotted showing these several effects. 

 As some of these effects were small, and as 

 oniy one variable was altered at a time., 

 very accurate measurements were required 

 to determine the effects in question. 



In the testing of direct-current instru- 

 ments the bureau is now prepared to handle 

 apparatus of capacities up to 1,000 amperes 

 and 1,000 volts. A larger storage battery 

 is being installed, which will give currents 

 up to 5,000 amperes at 4 volts or 10,000 

 amperes at 2 volts, and a high potential 

 battery of several thousand volts will be 

 installed in the near future. 



Section 5. Photometry.— One of the 

 rooms of the temporary laboratory of the 

 bureau was early assigned to photometric 

 work, and an equipment of apparatus 

 provided for measuring mean horizontal 

 candle-power of incandescent lamps. The 

 work was inaugurated by Dr. "Wolff, but is 

 now in charge of Mr. Hyde. As soon as 

 the new buildings are occupied this equip- 

 ment will be greatly augmented and the 

 Avork enlarged. After doing considerable 

 preliminary work the bureau is now pre- 

 pared to test and certify incandescent 

 lamps to be used as standards, and has 

 already done this in a ninnber of cases for 

 manufacturers and others. 



The Hefner amyl-acetate lamp has been 

 somewhat genei'ally accepted as a primary 

 photometric standard, but its numerous de- 

 fects make it quite unfit for a working 

 standard. After taking the most elaborate 

 precautions to maintain a steady and uni- 

 form flame, and applying corrections for 

 the pressure and humidity of the air and 

 its carbon dioxide content, the best results 

 of the most skillful observers differ many 



