\... lil 422. 



Moving Coil Mirror Galvanometers. String Galvanometers. 



891 



Moving Coil Mirror Galvanometer of max. sensitivity, Figure, with two different groups I s. d. 

 of windings on the same coil, one of which can be used for damping, with a fixed damping 

 resistance. The second group of windings in Xos. 61,412 61,414 is approx. one-tenth 

 the resistance and sensitivity of the main group. Fig. 61,412 A shows the connections 

 of Xos. 61,412 61,414, the arrangement for ballistic measurements being shown dia- 

 grammatically in the illustration. The instruments are provided with polished plane 

 mirror. 



61,417. Extra Price for Oil Damping, for enabling the instrument to be used at places which 

 an- not anti-vibrating 



6 1.4 is. Extra Price for Xos. 61,412 61,414 if provided with arrangement for increasing the 



l>crind of -wing to approx. 15 seconds for ballistic purposes 



1.13.0 



0. 18.0 



6 1.4 in. Extra Price for Xos. 61,415 and 61,416 for two entirely separate windings which can 



be connected up in any desired manner 1. 2.0 



til. 42d. Extra Price for a Mirror Chamber with Telescope the axis of which is placed at 45 



to the mirror plane 4. 10. 



61,421. Extra Price for a Telescope with Scale on turning arm which can be extended to 



V-2 metre 4. 0. 



tii.122. Large Einthoven Electro-Magnet String Galvanometer, improved type, Figure. 



very sensitive with extremely short period of swing. Price without microscope . . . 47.10.0 



A silvered quartz fibre of high resistance is stretched between the cimeiformly pointed pole 

 pi'-ei-s of a powerful electro -magnet. The current-sensitivity of the instrument can be varied by 

 regulating the voltage. The deflections of the quartz fibre traversed by the current in the magnetic- 

 field can be observed through a microscope let in through the holes of the pole pieces. 



The instrument is of anti-vibration type and independent of external magnetic influences, and 

 possesses a very short period of swing. It in suitable for a large number of fine measurements, e. g. : 

 (1) determining the conductivity of the air produced by uranium and radium preparations; (2) mea- 

 suring currents produced by atmospheric electricity; (3) ballistic measurements of small quantities of 

 l"<-trieity: : 4 ) measurements on telephone currents and nerve currents. Arrangements for registering 

 on s'-nsitive paper can easily be adapted to the instrument. 



With a magnification of x 1000 and employing the thinnest quartz fibre, the following sensi- 

 tivity can be attained: 0.1 mm = 1 xlO-> 2 amp. A correspondingly lower sensitivity is obtained 

 with the use of platinum, gold, silver, and copper wire. Further particulars of these on application. 



Cl. 30 F. 



