176 



Hartmann & Braun, Bockenheim- Frankfort o. M. 



Both instruments are provided with arrangements for compensating 

 influences of external temperature. 



82. Electrostatic Voltmeter for high voltage, in circular case. 

 By the peculiar shape and arrangement of the working parts the 



intervals of the scale are rendered nearly proportional. Range from 

 1 to 10-fold, between 100 and 50000 volts. 



83. Aperiodical Voltmeter and Amperemeter for continuous 

 currents on Deprez's principle. In circular case. 



84. Differential Voltmeter for controlling the voltage in the 

 two circuits of three wire systems. 



85. Universal Voltmeter for controlling the voltage in central 

 electric light installations, for continuous and also for alternating currents 

 with scale divisions visible at a great distance; scale embracing the 

 range of voltage of a particular plant. Two sizes of 50 and 35 centi- 

 meters diameter. 



87. 



86. Contact Voltmeter with minimum and -maximum efficiency, 

 for giving visible and audible signals or for actuating automatic voltage 

 regulators and cell switches, in the latter case with the aid of inter- 

 mediate Relais. 



87. Signalling Voltmeters with direct reading of the normal 

 voltage. Incandescence of a green lamp signifies that the voltage has 

 become too low, that of a red lamp that it has risen too high. An 

 alarm bell is sounded at the same time. 



88. Voltmeter for special purposes, e. g. for testing accumu- 

 lators, for electro-plating, for ships, railways and tram-cars, in various 

 forms according to the special purpose. 



