168 Hartmann & Braun, Bockenheim- Frankfort o. M. 



Standards made according to the standards in 



possession of the Imperial Physical and Technical Institute, 



Berlin - Charlottenburg. 



In the case at the left hand side entrance. 



32. Clark's Standard Cell. The mercury electrode formed by 

 amalgamated platinum, is sealed in a porous pot together with the mer- 

 curous sulphate paste, by which means the cell is rendered portable. 

 A thermometer dipping into the cell has its scale outside. The glass 

 is protected by a metal casing. E. M. F. = 1.438 (15 0.) 



33. Standard Resistances, of 0.1, 1, 10 etc. up to 10000- 

 ohms, made of manganine or constantan i. e. a material the coefficient 

 of temperature of which may be neglected, with nickel plated electrodes 

 for immersion in mercury cups. 



The resistance coils are accurately calibrated and soldered with silver to 

 the electrodes contained in perforated metal cases. Paraffine baths may therefore 

 be used for measurements at constant temperatures. 



34. Standard Resistances, 0.01, 0.001 and 0.0001 ohm, which 

 may also be used as shunts for exact current measurements; made in a 

 similar manner to those described in 33, excepting, that thin laminae 



are substituted for the 

 wires; fitted, apart of 

 the electrodes, with 

 two binding screws, 

 which branch off at 

 the exact terminals of 

 84< tT 11 i( IBIMHHP 8 * ^3Fr H\ i! 1 the resistances. 



0.001 and 0.0001 are- 

 contained in entirely 

 closed metal cases fitted 

 with cooling worm and 

 stirrers for parafh'ne 

 filling. 



35. Paraffine baths with nickel plated double mercury cups r 

 suitable for 2 to 4 standard resistances, with stirring apparatus driven 

 by a tiny electromotor. 



36. Small Compensation Apparatus containing a Clark stan- 

 dard cell and high ballast resistances (100 000 ohms), a commutator 

 switch and a very accurately adjusted resistance box also of 100 OOO 1 

 ohms; the latter is adjustable up to 10 000 ohms by plugs and cranks r 

 by means of which the resistances which are to be placed in the com- 

 pensation circuit may be found. Very intelligible and compact arrange- 

 ment and convenient manipulation. 



37. Large Compensation Apparatus. Similarly arranged but 

 with entire adjustable resistance box and having besides an equalization 

 resistance, whereby the correction of the temperature in the Clark 

 cell is introduced into the apparatus which thus becomes direct reading. 



