June 24, 1904.] 



SCIENCE. 



945 



densers has been made, including the meas- 

 nrement of their, capacities by different 

 methods, the effect of time of charge upon 

 tlieir measured capacity, and the deter- 

 mination of absorption, leakage and tem- 

 perature coefficients. ' Condensers have been 

 purchased from various makers in Eng- 

 land, France, Germany and America, and 

 comparisons made with a view of deter- 

 mining the best performance to be obtained 

 from both mica and paper condensers when 

 used as measures of capacity. Some very 

 interesting and valuable results have thus 

 been obtained, although the work is not yet 

 completed. Two large air condensers have 

 recently been constructed to be used as 

 standards. A new form of rotating com- 

 mutator for use in detennining capacities 

 in absolute measure has recently been com- 

 pleted in our instrument shop and has been 

 used in this work. 



A considerable number of standards of 

 inductance have been acquired and a great 

 deal of work has been done in comparing 

 inductances and determining their values 

 absolutely. The bureau is now in a posi- 

 tion to make accurate measures of both 

 capacity and inductance and to compare 

 and test condensers and inductance stand- 

 ards for the public. 



Section 4. Electrical Measuring In- 

 struments. — This section includes both al- 

 ternating and direct current instruments 

 (including instruments for measuring 

 heavy current and high potential) except 

 those precision instruments included in 

 Section 1. Some testing of ammeters, volt- 

 meters, wattmeters and watthour meters 

 has been done for the public, but the prin- 

 cipal work done so far has been prepara- 

 tory. Many instruments have been pur- 

 chased from the best instrument-makers at 

 home and abroad, and other instruments 

 have been designed and built in our own 

 shop. Much of the apparatus purchased 

 has been tested and in some cases altered 



and improved. Methods of measurement 

 have been investigated, and a considerable 

 experience acquired preparatory to the 

 equipment of the laboratory for this work 

 in the new building, to which this work has 

 recently been transferred. 



In addition to direct-current generators 

 and storage batteries the following equip- 

 ment of generators for alternating current 

 has been acquired : 



1. A small 120-cycle alternator, single- 

 phase, suitable for voltmeter or condenser 

 testing. 



2. A three-phase 120-cycle alternator 

 driven by an inverted rotary used as a 

 motor and itself capable of giving a three- 

 phase 60-cycle current. 



■ 3. A pair of 60-cycle three-phase revolv- 

 ing field alternators (direct-connected to 

 a driving motor), of which one can have its 

 armature rotated by a hand wheel while 

 running, so that its current is displaced in 

 one phase with respect to the other. Using 

 one of these generators for the main cur- 

 rent (which by use of transformers may 

 be multiplied at reduced voltage) and the 

 other for the potential current, any desired 

 power factor may be obtained and watt- 

 meters and watthour meters conveniently 

 tested up to a capacity of 1,000 amperes 

 and any desired voltage. 



4. A pair of two-phase alternators, sur- 

 face-wound and giving currents of nearly 

 sine wave form (direct-connected to a driv- 

 ing motor), one alternator giving 60 cycles 

 and the other 180, arranged so that the two 

 armatures may be placed in series and the 

 wave form varied through a considerable 

 range by varying the magnitude and 

 phase of the third harmonic. This is use- 

 ful in studying the effects of varying wave 

 form on the indications of measuring in- 

 struments of different kinds. For study- 

 ing the effects of variations of frequency 

 the speed can be varied through wide 

 limits, and, for higher frequencies, the 



