1914] 



on Fluid Motions 



81 



The apparatus consisted of two aspirator bottles (Fig. 10) con- 

 taining water and connected below bj a passage bored in a cylinder 

 of lead, 7 cm. long, fitted water-tight with rubber corks. The form 

 of channel actually employed is shown in Fig. 11. On the up- 

 stream side it contracts pretty suddenly from full bore (8 mm.) to- 

 the narrowest place, where the diameter is 2-75 mm. On the down- 

 stream side the expansion takes place in four or five steps, corre- 

 sponding to the drills available. It had at first been intended to 

 use a smooth curve, but preliminary trials showed that this was 

 unnecessary, and the expansion by steps has the advantage of bringing 



L«T.-.^..v^-ej.W-T.lV^S^ * 





i 



^^VA^^^V'A^^^^•I^O[^^v • \v\r" rr" rrrr- - ^^rF • •A^^" • • • • • • • • •»•-•.■•———•••••••••—••- 





.•.'.-.'.'.•.T/^YXV 



Fig. 10. 



before the mind the dragging action of the jets upon the thin layers- 

 of fluid between them and the walls. The three pressures concerned 

 are indicated on manometer tubes as shown, and the two differences 

 of level representing head and suction can be taken off with com- 

 passes and referred to a millimetre scale. In starting an observation 

 the water is drawn up in the discharge vessel, as' far as may be 

 required, with the aid of an air-pump. The rubber cork at the top 

 of the discharge vessel necessary for this purpose is not shown. 



As the head falls during the flow of the water, the ratio of head 

 to suction increases. For most of the observations I contented 

 myself with recording^ the head for which the ratio of head to- 



Vol. XXI. (No.^ 108) a 



