Hartmann & Braun, Bockenheim- Frankfort o. M. 



161 



3. Apparatus for measuring high insulation resistances 



consisting of an astatic cable galvanometer with Bruger's magnets, 

 several shunt resistances, a scale lamp for objective reading, a megohm 

 with 10 subdivisions as standard of comparison, a battery of dry accu- 

 mulators with universal pachy trope and switches. 



4. Apparatus for measuring capacities ol cables, consisting 

 of a ballistic reflecting galvanometer with Weber's magnets, a reading 

 telescope, a condenser of one microfarad with subdivisions, together with 

 -charge and discharge keys. 



The reflecting galvanometers of the preceding four groups are mounted 

 upon isolated brick piers, the optical reading appliances belonging to them are 

 placed upon adjustable Gauss stands. 



Upon tables arranged along the walls. 



5. Apparatus for measuring small resistances, in particular, 

 for testing the conductivities of materials, consisting of a resistance 

 bridge with key, amperemeter and sensitive galvanometer. Range from 

 O.00001 to 5 ohms. 



The measurements are made on the principle of the Wheatstone bridge, 

 modified, however, in such a manner that by double reading the intermediate 

 resistances are eliminated. The result is obtained without extensive calculation 

 -by direct reading from the scale of the apparatus. By means of universal 

 clamps conductors of any section and also carbons may be placed in the circuit. 



6. Apparatus for testing iron and steel with respect to magnetic 

 permeability and coercive properties, consisting of a standard electro- 

 magnet, a Lenard's bismuth spiral, a bridge for determining the strength 

 -of the magnetic field, a galvanometer constructed on Deprez's principle 

 -and an amperemeter. 



11 



