Chambers 2½ inches and 4 inches in diameter have been constructed of brass with pyrex ports and sealed with lead‐wire gaskets. Metal walls and a copper heat leak eliminate the need for a surrounding pressurized bath. The required fast‐pulsing techniques and use of a heat regenerator are described in detail. Schematic diagrams show the chambers, pressure‐ and temperature‐monitoring devices, and illumination method, and photographs of typical tracks and events are included.