Prof. Magnus's Hydraulic Researches. 177 



Formation of drops. 



16G. If water be suffered to flow through a tap so that its 

 velocity may be altered at pleasure, and if the tap be so adjusted 

 that the drops are formed separately and at rather long intervals 

 of time, the drops are seen at first to assume the form of fig. 15 

 if the efflux-opening has a diameter of 8 millims. : this agrees 

 with Savart's representation. They then contract, as is shown 

 in fig. 16, and immediately afterwards they fall. If this pro- 

 ceeding be watched by means of the rotating slit, it is seen how, 

 at the moment of dropping, a thin narrow thread of water [a b, 

 fig. 17) is formed out of the contracted portion which connects 

 the drop with the residual water. From this thread are gene- 

 rally produced two or more smaller drops. 



1G7. More than one of these small drops are produced if the 

 greater drops are formed in somewhat quicker succession. The 

 residual liquid {a, fig. 17) is seen then after each separation to 

 move backwards and forwards ; and if during these undulations 

 the new drop is separated, smaller drops are produced in greater 

 number ; nor do they then all fall vertically. 



It is not difiicult to understand how such undulatory motions 

 give rise to irregularities in the separation. Similar irregular 

 motions doubtless give rise, even in a stream without swellings, 

 to small laterally-moving drops (§§ 118 and 158) at the extreme 

 end of the continuous portion. 



168. If the formation of the drops be accelerated by adjusting 

 the tap so as to gradually increase the flow of water, the drops 

 are suddenly transformed into a continuous stream. Drops are 

 also formed from this, but only at its extreme end. Moreover, 

 in comparison with those which were formed quite close to the 

 efflux-opening, they are very small, because the diameter of the 

 stream rapidly decreases. It is sometimes possible so to adjust 

 the tap, that the drops are formed at the efflux-orifice itself, but 

 following one another with a velocity almost equal to that with 

 which they are transformed into a continuous stream. In this 

 condition only a slight percussion is required to effect this trans- 

 formation and to cause the sudden junction of the drops. It is 

 then very remarkable to observe how very different is the size of 

 the drops which are formed in the two cases. 



These phjenomena, which have doubtless been frequently ob- 

 served, explain, as I imagine, the formation of the smooth con- 

 tinuous part of the stream, as well as that of the small laterally- 

 moving drops in the stream without swellings. 



The form of swelUiujs which arc disturbed by solid bodies. 



169, I cannot avoid mentioning some singular forms assumed 

 Phil. May. S. v. Vol. 18. No. 1 10. ,SV/>/. 1859. N 



