Hartmaim & Braun, Bockenheim- Frankfort o. M. 167 



sired degree. A small reading telescope is directly attached to the in- 

 strument. Degree of precision: 1 : 10000. 



28. Simple Local Variometer for measuring local changes of 

 the horizontal intensity. Only one instead of four deflection magnets; 

 a simple needle instead of a magnetic mirror; otherwise similar to 

 27, but of greater portability. Degree of precision: 1 : 1000. 



29. Absolute Bifilar Suspension Magnetometer. By exact 

 measurement of the relatively great distance of 12 mm between the 

 wires, the deflections due to the reversal of the tubular magnet give 

 the product of the magnetism of the bar magnet and the terrestrial 

 magnetism in absolute measure. Simultaneous observation made with 

 a nnin'lar suspension magnetometer gives the intensity of the terrestrial 

 magnetism in absolute measure. The advantages of the method consist 

 in rendering the measurement of time and of the influence of tempe- 

 rature dispensable. 



30. Absolute Bifilar Suspension Galvanometer. The magnet 

 is replaced by a wire ring of many convolutions which may be measured 

 exactly. The deflections of this ring due to a current represent the 

 product of strength of current, area of circuit and terrestrial magnetism. 

 This instrument may be used for absolute measurements of currents or 

 terrestrial magnetism by using it in combination with an absolute 

 tangent galvanometer or a single suspension magnetometer. 



31. Spring Galvanometer. A tube of thin sheet iron sides is sus- 

 pended by a torsionless spiral of many convolutions and is drawn into 

 & solenoid by the current. The amount of the attraction is seen from 

 a scale divided, in amperes. The indications are aperiodical and in- 

 dependent of strong extraneous currents. The instruments are adapted 

 for currents up to 3000 amp. 



