Abstract: The invention relates to the measurement of the shade of a particle. The particle is illuminated with light of variable intensity and viewed against a background level of illumination. A measurement is made of the ratio of time for which the intensity of light from the particle exceeds the intensity of the background to obtain a measurement of the shade of the particle.

Abstract: The colors or surface conditions of small articles are determined by passing the articles through an integrating sphere and separately illuminating the articles before they enter the sphere, during their passage through the sphere and after they leave the sphere. The light transmitted through or reflected by each article is collected by the sphere and passed to analyzing apparatus. The articles are sorted according to the measurements.

Abstract: A method of cutting a material, which may be insulating or conducting, which includes the steps of placing a pair of parallel spaced electrodes, preferably taking the form of a pair of wires, close to or in contact with the material, applying a voltage across the electrodes and causing relative movement between the electrodes and the material as the spark erodes the material to effect the cut. The invention also provides apparatus for carrying out this method.