The alterations in design of a Wilson‐Blackett automatic cloud‐chamber apparatus, found necessary or convenient in adapting it to photographing tracks of high‐speed ions from a high‐voltage tube, are briefly described. An experimental cloud‐chamber, which can be oriented in any position, constructed from a six‐inch diameter metallic sylphon‐bellows, free from leaks and with several other advantages, is shown. A convenient type of mercury spark‐lamp which makes possible the use of fine‐grained positive‐emulsion films is described. Designs are given for a larger sylphon‐type chamber based on the satisfactory experience with the smaller chamber.