Drawings from his patent (#73229) for the spirometer dated 1868.  From this It is apparent that it is a rectangular water-seal spirometer.  It was made of tin plate and its dimensions are listed as 8-1/2 inches wide, 4-1/2 inches deep and 13-1/2 inches tall.  The wire “handle” that projects over the top was a guide for the inner spirometer reservoir (bell).  The index (ruler) was attached to the inner reservoir and had a cover that protected it from wear.  A 1/4″ of vertical movement was equivalent to 8 cubic inches.  He specifically claimed that the guide rods and shield for the index were unique to his invention.