182 Prof, Magnus's Hydraulic Researches. 



easily pressed to tlie side, because there are fewer particles near 

 them whose inertia they have to overcome. Hence they oppose 

 less resistance to a force acting at right angles from without 

 than the less projecting parts. 



For the same reason, at those parts where the radius of cur- 

 vature is negative, the resistance to a force acting at right angles 

 from without is greatest when the radius of curvature is least. 

 In a square aperture, the particles falling from the corners of the 

 squares experience a less resistance in a horizontal direction than 

 those descending from the sides. The particles of water coming 

 from the projecting places experience a less resistance in passing 

 from the edge of the aperture to the cross section underneath, 

 and from this to a second, and so on, than the others. On account 

 of this smaller resistance, the motion of the particles coming 

 from the projecting parts of the orifice is more horizontal; and 

 these particles reach the deeper ci'oss section of the jet with less 

 inchnation than those from the less projecting. parts, and con- 

 sequently produce a greater pressure against the liquid in the 

 deeper cross section. 



67. In the same manner, the cohesion or attracting force 

 which takes place between the particles of the liquid acts so, 

 that if the aperture be not circular, the directions of the particles 

 coming from the edge of this orifice are not all changed alike ; 

 for in consequence of this mutual attraction, the particles in any 

 cross section of the jet would only be in equilibrio if the cross 

 section were circular. Hence, in the cross sections which are 

 not circular, there results a motion by which the perimeter is 

 speedily changed into the circumference of a circle. But this 

 motion is not the same for all particles in the same perimeter. 

 Those which are at the prominent points, or where the radius of 

 curvature is positive and least, are attracted with greater force 

 to the interior of the jet, than those at the points where the 

 radius of curvature is negative. 



Hence the particles coming from the projecting places also 

 experience, in consequence of the cohesion of the liquid, a less 

 hindrance to their horizontal motion than those coming from 

 other points, and assume, in consequence of this mutual attrac- 

 tion, a more horizontal direction than the latter. 



68. Having a more horizontal direction, the pressure also 

 which the particles falling from the prominent places of the 

 aperture exercise on the interior of the jet, is greater than that 

 which the I'est produce. This greater pressui'e can even produce 

 a cavity in the jet. This can be best observed by using an aper- 

 ture of the form fig. 20, wherewith the water coming from the 

 part bd produces a considerable cavity in the jet. Fig. 20 a 

 represents a vertical section. The particles of water coming 



