Page:The Armed Forces Institute of Pathology-ItsFirstCentury.djvu/59

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powers of magnification, or those requiring extended exposure, the beam of light was passed through a pane of greased ground glass giving a diffused "white cloud" effect or, where necessary, through an achromatic condenser placed below the stage. Photographs were made with violet light, separated from the mean white light of the sun by passing the beam through a blue ammonio-copper solution, which also aided the operator by absorbing the heat