PEIRCE. 



OSCILLATIONS OF SWINGING BODIES. 



77 



crease of amplitude is gradual, is clearly shown. The two curves 

 show different values of the original deflection. 



The Damping of the Slow Oscillations of a d'Arsonval 

 Galvanometer Coil, which is wound on a Nonmetallic 

 Core, and is swinging between the Poles of its Magnet. 



If the coil of a d'Arsonval galvanometer be wound on a wooden 

 spool, and if its circuit be open, the damping of its oscillations is due 

 principally, unless the copper wire is magnetic, to air resistance, and 



TIME. 



Figure C. 



only slightly to frictional forces within or at the surface of the gimp 

 from which the coil hangs. When, however, the circuit of the coil is 

 closed through an outside resistance x, electromagnetic damping is 

 added, and the damping coefficient of the motion is larger than before, 

 or, if x is small enough, the motion ceases to be periodic. In many 

 instances it is possible and desirable to damp the coil critically, but 

 this is sometimes impracticable, — as, for instance, in such instru- 

 ments of long period (400 or 500 seconds) as are used in testing mas- 

 sive iron cores, — and there are certain kinds of absolute measurements 

 where a relatively undamped instrument is preferable. The throw of 



