260 W. R. HEBBLEWHITE. 



A given rate of flow of air will require a certain number 

 of holes by which to escape. The air will, therefore, lift 

 the float until sufficient holes appear above the water level 

 to allow of its discharge. An increase in rate of flow will 

 cause a further rise of the float, and a decrease will cause 

 a fall of the float, since the pressure of the air is governed 

 by the height of the float in the water. Any height of float, 

 when equilibrium is maintained, will correspond to a 

 definite rate of flow of air, and to a definite pressure differ- 

 ence between inside and outside the float. 



3. Construction.— The instrument constructed for the 

 laboratory (Fig. 1 and Plate XII), consists of a brass con- 

 taining vessel 6" diameter, 12" high, mounted by brackets 

 on a vertical wooden stand. The float is 4" diameter, and 

 is made of No. 36 gauge sheet brass soldered to shape. At 

 its base it carries a buoyancy chamber 5J" diameter out- 

 side, with a central opening 1" diameter through which the 

 air inlet pipe passes. The depth of this chamber is If". 

 The effect of this air-tight chamber is to nearly balance 

 the weight of the float in the water, reducing the pressure 

 under which the air escapes. The air enters the float by a 

 f" inlet pipe passing through the base of the containing 

 vessel, to which it is permanently fixed. This pipe passes 

 to level with the top of the vessel. The end is plugged, 

 and the air passes from it through holes in the circumfer- 

 ence at the top, thus preventing gusts of air impinging on 

 the top of the float and disturbing its equilibrium. The 

 float's motion is constrained to a vertical direction by two 

 pairs of pulleys carried on pivot bearings, the lower pair 

 being mounted at the top of the containing vessel, and 

 running on light brass guides attached to the sides of the 

 float. The upper pair are mounted on the main base-board 

 about 14" above the top of the vessel, and between them 

 runs a single circular guide standing from the centre'of the 

 top of the float. 



