Hartmann & Braun, Bockenheim- Frankfort o. M. 



173 



Electrical Measuring Instruments for School Purposes. 



In the following instruments particular attention has been paid to 

 simplicity and intelligible arrangement of the parts and care has been 

 taken to render the movements of the pointers and the divisions on the 

 dial distinctly visible from a distance of 10 meters. 



63. Lecture Galvanometer with bell magnet, powerful damper, 

 with pointer; interchangeable multipliers; also for use as a differential 

 galvanometer. The pointer magnet may be replaced by a reflecting 

 magnet. The galvanometer may thus be used as a reflecting galvano- 

 meter for projection on the screen or for telescopic reading. 



64. Simple Lecture Galvanometer, with 2 bar magnets, one of 

 these, the astatizing magnet, being detachable. The whole instrument 

 can be taken to pieces. 



65. Resistance Bridge with stretched measuring wire of 1 meter 

 length, divided in half decimeters for the audience and in millimeters for 

 the purposes of the lecturer. 



66. Open Wire Coils, wound 

 so as to obviate self-induction, of 1 

 and 10 ohms, forming comparison 

 resistances. 



88. 



67. Lecture Voltmeter. Iron core drawn into solenoid. Coun- 

 teracting spring. The rectilinear movement is by means of a lever 

 transmitted to the centre of the pointer. Eange 0.5 to 3 volts. Also sui- 

 table for measuring the voltage of single cells. By means of an additi- 

 onal resistance the range may be increased 10 times. 



68. Lecture Amperemeter, similar construction, range 0.2 to 2 

 amperes, with shunt up to 10 amperes. 



69. Induction Apparatus. The secondary coil is detachable and 

 the iron core may be replaced by a magnet. The apparatus is adapted 

 for Faraday's experiments on induction. 



70. Telephone having all its parts exposed to view, forming an 

 alternating current galvanometer for measurement of fluid resistances, 

 -e. g. the internal resistances of cells in connection with bridge 65 and 

 induction apparatus 69. 



