170 



Hartmann & Braun, Bockenheim- Frankfort o. M. 



42. Ballistic Reflecting Galvanometer, according- to Weber's 

 arrangement, with short tube magnets and interchangeable multiplier. 

 Adjustable duration of oscillations : 15 seconds. 



Sensitiveness at 50 ohms: 1 mm*) = 0.00000002 amp. 



43. Large dead beat Reflecting Galvanometer. Eigid struc- 

 ture; bell magnet in lentiform copper damping shell, may be interchang- 

 ed for a ring magnet; double wound multiplier with rack and pinion 

 movement; astatization by means of a ring of soft iron. In this instru- 

 ment are combined the special features of the types of Siemens, Wiede- 

 mann, du Bois-Eeymond, Becquerel and Braun. 



Sensitiveness without astatization at 400 ohms: 1 mm*) 

 0.00000007 amp. 



44. Simple dead beat Reflecting Galvanometer, similar in 

 construction to 43, but a little smaller and simpler. Multiplier arranged 

 to be moved by hand. Suspension by quartz thread. 



Sensitiveness: nearly the same as with 43. 



45. Astatic Aperiodical Reflecting Galvanometer. Bruger 

 magnets consisting of the two coupled halves of a vertically suspended 

 hollow cylinder, which combine the advantage of diminished inertia with 

 considerable magnetic momentum and high degree of astatization. 

 Suspension by quartz thread. Damping adjustable within wide limits. 

 Conveniently set up; fitted with small telescope, 50 cm distance, directly 

 attached to instrument, so as to render the instrument available for out- 

 door use. 



Sensitiveness at 5000 ohms and 15 seconds duration of oscillations: 

 1 mm*) = 0.0000000025 amp.. 



*) With reflecting galvanometers the sensitiveness refers always to a 

 deflection of 1 mm at a distance of scale of 1 meter. 



