When it vibrates in several sections, each section moves in the opposite way to its neighbours.
This hammer is arranged so that when the armature vibrates it gives little blows to the underside of the tube and shakes up the filings.
Therefore with equal weights a balance vibrates more slowly the more sensitive it is, and therefore weighing by a sensitive balance is a slower process than with a less sensitive one.
To find the radius of the sphere of water which vibrates seconds, put p = 21I, T= 81, p= 1, n= 2.
Now if a be the amplitude expressed in millimetres, and t the period expressed in seconds, then the maximum velocity of an earth particle as it vibrates to and fro equals 27ra/t, whilst the maximum acceleration equals 4,r 2 0 2.