186 Prof. Magnus's Hydraulic Researches. 



The aspect of such a continuous jet, 2'^'5 long, is very 

 beautiful. It appears hke a perfectly turned solid mass of the 

 whitest glass, for there is not the slightest motion perceptible. 



77. That in a jet issuing from a circular orifice there are no 

 dilatations perceptible in the immediate neighbourhood of the 

 orifice, is evident from the explanation j ast given of the form of 

 jets issuing from a quadratic or polygonal aperture. For since 

 in a circular jet the resistance in all directions is the same, and 

 all parts of the liquid pass over the edge of the orifice with equal 

 velocity, the resistance for all parts is the same, and no part of 

 the jet can be pushed more forward than another. 



78. But if the afSux of the liquid does not take place with 

 equal velocity from all sides of the vessel, either because the edge 

 of the aperture is not quite smooth, or because the aperture is 

 too near one wall of the vessel, or because it has been made in a 

 wall of the vessel, and its diameter is so great that the liquid 

 flows out at the lower edge with a greater velocity than at the 

 upper one, or because other hindrances occur, then dilatations 

 are formed even in a circular jet in the immediate neighbourhood 

 of the aperture. By placing a piece of sheet-metal at the bottom 

 of the vessel near the orifice they may be perceived. 



79. These dilatations or ventral segments are, however, not 

 to be mistaken for the ventral segments which Savart has de- 

 scribed*. The latter, to which I shall afterwards, § 81, return, 

 are formed only when the liquid has ceased to be continuous ; 

 while the dilatations are formed at a very small distance from 

 the aperture, where the jet is still perfectly continuous. These 

 ventral segments differ from those of Savart, in so far that the 

 latter form surfaces of rotation, while the ventral segments under 

 notice have no circular sections. 



80. If the water be allowed to issue from a circular aperture 

 tranquilly and without any perceptible disturbance, but without 

 using the tranquilizer, §38, the rotation, mentioned at § 37, occurs 

 in the vessel after some time, and the jet assumes a small spiral 

 form, which is first perceived at the parts most distant from the 

 efflux orifice. This is of course present in the upper part of the 

 jet, but it is not visible : only after some time, when it is toler- 

 ably marked in the lower part, is it perceptible above, and thus 

 it has the appearance of spreading from below upwards. After 

 some time the whole jet appears like a twisted rope, and although 

 it issues from a circular orifice, it is quite similar to the jet from 

 an elongated quadrangular orifice, § 51, fig. 16 « and b, except- 

 ing that it is not deflected like that, but falls down vertically. 

 After what has been said, § 52 to § 58, on the origin of such 

 spirally formed motions, this needs no further explanation. Every 



* Annates de Chimie et de Physique, 2ucl series, vol. liii. p. 337. 



