96 PHYSIOLOGICAL PHYSICS. [Chap. x. 



the needle in the opposite direction, and by this 

 means its effect on the needle will be increased. This 

 application of the principles of Oersted arid Ampere 

 was made by Schweigger in Germany in 1820, who 

 coiled the wire on a rectangular frame (Fig. 50). By 

 coiling the wire on the frame oftener than once the 

 effect of the current is increased, provided that each 



turn of the wire be carefully insulated 

 from the other. Thus an instrument 

 called a MULTIPLIER is constructed, 

 by means of which a weak current, 

 which might not have any effect 

 on a needle, has its action so in- 

 Fig. 50. Multiplier, creased that deflection of the needle 



occurs. This instrument can now 

 be used as a means of detecting the presence of a 

 current. By its means not only the presence, but 

 also the direction and the amount of a current can be 

 estimated. Hence the term GALVANOMETER applied 

 to the instrument. Its developments are described in 

 the next chapter. 



CHAPTER X. 



GALVANOMETERS. 



THE tangent galvanometer is an applica- 

 tion of the principle laid down by Schweigger. It 

 is formed of a vertical circle standing in the plane of 

 the magnetic meridian. The circle may be formed of 

 a ribbon of copper, or may consist of a wooden frame 

 with several turns of copper wire (each turn being 

 insulated) wound upon it. The ends of the wire are 

 connected to whatever is producing the current. In 

 the centre of the circle is mounted horizontally a 



