The air with which this spray was blown was first rendered dust-free by passage through a tube containing glass wool. The minute droplets of oil constituting the spray, most of them having a radius of the order of a one-thousandth of a millimeter, slowly fell in the chamber
, and occasionally one of them would find its way through the minute pinhole
in the middle of the circular brass plate
, 22 cm. in diameter, which formed one of the plates of the air condenser. The other plate,
, was held 16 mm. beneath it by three ebonite posts
