# Page:Popular Science Monthly Volume 83.djvu/447

and the plate ${\displaystyle B}$ so that ${\displaystyle B}$ may be stopped in any position. When the crank is turned ${\displaystyle B}$ passes alternately in front of and parallel to ${\displaystyle A}$ and ${\displaystyle C}$. The contacts are so arranged that when ${\displaystyle B}$ is parallel to ${\displaystyle A}$ it is joined to earth and so charged oppositely to ${\displaystyle A}$. It is then revolved in front of ${\displaystyle C}$, at which instant ${\displaystyle C}$ is joined to earth and is charged by induction oppositely
to ${\displaystyle B}$ and like ${\displaystyle A}$. As ${\displaystyle B}$ again comes in front of ${\displaystyle A,A}$ and ${\displaystyle C}$ are joined and ${\displaystyle B}$ is earthed. ${\displaystyle B}$ now receives by induction a greater charge than before, since ${\displaystyle A}$ has now received the greater part of ${\displaystyle C}$'s charge. By successive revolutions of ${\displaystyle B}$ the charge may thus be built up to any desired intensity upon ${\displaystyle A}$.