Abstract
An instrument has been devised which will measure continuously the charge and dimensions of individual ice crystals or water droplets within clouds at ground level. If its collection efficiency for cloud particles were established it could then also be used to determine particleβsize distributions and volume charge densities inside clouds.
A collimated beam of particles passes through a transverse electric field before impinging on a moving belt of 35 mm film coated with Formvar which has been softened immediately prior to exposure to the beam. Each particle is deflected by an amount proportional to its chargeβtoβmass ratio. The dimensions, type and charge of each collected particle can therefore be determined by subsequent analysis of the replicas using a stopβmotion projector allied to a data recording system. If required, the dimensions of selected particles can be determined more precisely using an electron scanning microscope. The minimum detectable charge on a droplet of radius r cm and terminal velocity V cm s^β1^ is given approximately by q~min~ βΌ 5 Γ 10^β2^ r^3^ V^2^ e.s.u.