Unpublished diagrams, experimental apparatus and results by William Lawrence Balls Seven diagrams, labelled figures 1-7, showing a graph of relative humidity of cotton-air, a diagrammatic representation of the air circuit in the 'CAM test', a hygrometer cabinet, a filter, the thermometer-guide inside the filter, a layout of Balls' 'CAMTEST' apparatus and a set of mounts for reading-lenses. Subject: Scientific apparatus and equipment [1939-1944]