166 



Hart-maim & Braun, Bockenheim- Frankfort o. M. 



23. Unifilar Suspension Electro-dynamometer for small currents 

 with mirror reading. The current is led to the movable bobbin by the 

 suspension wire and a platinum coil, acting as a damper, dipped into 

 dilute sulphuric acid. 



24. Portable Differential Galvanometer with mirror reading. 

 Provided with a small magnetic steel mirror suspended within the oval 

 multiplier. The amount of damping may be regulated by means of a 

 copper sliding piece. The sensibility is rendered variable by various 

 thicknesses of the duplex winding and by a controlling astatizing magnet. 

 Without astatization and with a resistance of 50 ohms a deflection of 

 1 mm reads 0.0000004 amp. at I meter distance of scale. 



25. Absolute Tangent Galvanometer. The current passes 

 through a copper ring which can be accurately measured. All unneces- 

 sary metal parts are avoided. The reflecting magnetometer, which is 

 free from metal, may be removed and replaced by a needle. 



26. Portable Bifilar Suspension Variometer for Terrestrial 

 Magnetism. Tubular strongly damped magnet suspended by two fine 

 wires placed a short distance apart. The constants are found by means 

 of a torsion circle provided with vernier and micrometer adjustment. 

 Expeditiously set up. Changes of position controlled by stationary 



mirror. 



27. Intensity Variometer for Terrestrial Magnetism. The 

 magnetic steel mirror is, by means of 4 small deflection magnets, placed 

 at right angles to the meridian, so as to neutralize the influence of 

 variation of declination. The sensibility may be regulated to any de- 



