174 



Hartmann & Baum, Bockenheim -Frankfort o. M. 



On the Platform in the centre of the room. 



71. Large Electromagnet with vertical bobbins, fitted with all 

 appliances for Faraday's experiments, also with 



72. Waltenhofen's Induction Pendulum and 



73. Lenard's Bismuth Spiral for measuring magnetic fields. 



74. Weber's Earth Inductor for determining terrestrial magnetic 

 inclination. A. magnetometer supplied with the inductor for adjusting 

 purposes renders it suitable for a tangent galvanometer. 



75. Astatic Oscillation Galvanometer according to Weber, for 

 observing inductive impulses by the earth inductor. Adjustable damping. 



76. Magnetometer according to Gauss and Weber, for deter- 

 mining the terrestrial magnetic declination and the horizontal intensity 

 by observations of oscillation and deflection. 



77. Reflecting Electrometer for measuring electro-static po- 

 tential differences. The peculiar arrangement and shape of the vane 

 renders the deflections proportional within wide limits. Ranging from 

 1 to 500 fold between 1 and 50000 volts. 



Industrial Direct Reading Instruments for large currents, 



for E. J\f. F. 3 Sy Intensity, 

 Insulation resistances., Energy expended. 



Displayed along the walls. 



78. Voltmeter and Amperemeter for continuous currents. 

 Circular cases, two sizes. Attraction of core of rolled sheet iron into 

 solenoid; torsion counter spring (compensation of temperature by double 

 spiral). Transformation of reciprocal in circular motion by means of 

 lever with jewelled pivots. The peculiar form of the iron core admits 

 of the form of the dial being varied at will. 



Range from 1 to 20-fold reading, numerous models for all currents 

 up to 3000 amp. 



