Prof. Magnus's Hydraulic Researches. 183 



from d move in almost a horizontal direction, dg, towards the jet 

 issuing from the circular part of the aperture, and in consequence 

 of the pressure which they exert, the concave surface gk is formed. 



69. Similar phaenomena to those with the aperture just men- 

 tioned are seen with all angular orifices, and especially with a 

 square one. The masses of water coming from the corners press 

 stronger against the interior of the jet than those coming from 

 the sides, and hence the former have the same relation to the 

 latter as single jets which move towards each other. By the 

 encounter of these jets is produced the tirst system of surfaces, 

 and from that all following ones in the same manner as with the 

 cruciform aperture, § 61, fig. 17. 



70. That the peculiar action which the parts of water coming 

 from the prominent places of the orifice exert is chiefly depend- 

 ent on the less resistance which the horizontal part of their 

 motion experiences from the mass of water contained in the jet, 

 is evident from the fact, that when the efflux is so arranged that 

 the parts of the liquid can only move in a vertical direction, this 

 action is no longer exerted. By using an aperture in a thick 

 wall instead of a thin one, the particles have, on leaving the 

 orifice, only a vertical motion. Hence the form of the jet can 

 only be changed by cohesion, and not by an inequality of resist- 

 ance. But the changes produced by cohesion alone are far less 

 than those produced by resistance and cohesion together. 



71. If the water be allowed to issue from a tube 25 millims. 

 long, and which has a square section as lai'ge as the aperture in 

 the thin wall, and if care be taken that the tube is completely 

 wetted and full, the jet assumes a circular section just on leaving 

 the tube, and has neither the ventral segments nor any of the 

 phaenomena which are presented by the jet issuing from a thin 

 orifice. 



The case is similar when, instead of the aperture, fig. 20, a 

 tube is used whose section is equal to this aperture. The jet 

 assumes then a section which is almost circular. Immediately 

 below the aperture it appears broader, which arises from the 

 fact that the particles issuing at d, fig. 20, although only acted 

 upon by cohesion, are yet pressed by it towards the interior of the 

 jet with a much greater force than are the other pai'ticles. The 

 jet once broader, contracts again, is again broader, and thus 

 these ventral segments are repeated several times. 



72. By this, the difference of the efflux from a thin or thick 

 wall is rendered clear. In using the latter, or a tube, and when 

 all the parts move vertically, cohesion alone acts, and produces 

 the changes of form. If, on the other hand, the aperture be 

 made in a thin wall, the particles of the liquid move not only in 

 the vessel in a more or less horizontal direction, but maintain 



