TO face page 44. 



FIG. 17. Pans for Equalizing Pressure. Two painted tin pans with rubber diaphragms which fit their interior are 

 attached to connecting air-pipe. Weight of diaphragms is equipoised by lead shot suspended from a bicycle 

 wheel. Variations in position of height of diaphragm are read on the graduated arc beneath bicycle wheel. 



Fio. 18. Apparatus for Analysis of Residual Air. U tubes on top shelf of table are connected 

 with Klster meter. Glass water-pump and air-separating chamber immediately to right of 

 center posts. Sulphuric-acid drying bottle at right of Elster meter. 



