142 THE MECHANICS OF THE EARTh's ATMOSPHERE. 



bility, so that small disturbances had only a rapidly diminishing in- 

 liaeuce upon their course. At the forward end of these jets there 

 formed peculiar surfaces of flow that plainly allowed the influence of 

 viscosity to be seen. These phenomena of motion are of remarkable 

 beauty and delicacy, of which any one may convince himself who per- 

 forms the easily repeatei! experiments. 



Since the theoretical investigations mentioned in the introduction 

 treat of the modilicaiions of jets by solid bodies, and Kirchhofl' 

 esi)ecially gives a series of interesting examples bearing upon this, 

 therefore this question has also been taken into consideration in my ex- 

 periments. Very stable forms of jets are also thus formed that have 

 more similarity with those deduced by theory than one could have ex- 

 pected. 



III. 



The experiments were made with the following simple apparatus: 



A cylindrical glass vessel (Fig. 9), of about GO centimetres height and 



12 ceutiuietres diameter, was tilled with water. Into this there passed 



a flow of water from a filter through an 

 India-rubber tube, a glass stop-cock, and a 

 glass tube. The Alter, as also the entire 

 tubular system, was tilled with the colored 

 liquid. After filling with water the glass 

 cylinder (in whose place one ujay also use 

 any large glass vessel), one must wait a long 

 time until the motion of the water has been 

 destroyed by viscosity. The experiment 

 succeeds best when the water has stood for 

 many hours in the cylinder, since then cur- 

 rents resulting from differences of temperature are no longer present. 

 By a quick opening of the glass stopcock one can allow a definite quan- 

 tity of colored liquid to enter into the quiet liquid, or by a longer 

 opening one can attain a steady stationary current. By elevating or 

 depressing the filter one can easily regulate the height of the upper 

 fluid level. The use of a small diflerence of pressure was found to be 

 the principal condition for the maintenance of regular current forma 

 tions. 



The majority of the experiments if no other problem was on hand 

 were executed with an excess of pressure of about liU millimeters. By 

 means of proper arrangements solid bodies could be oi)posed above the 

 jet. For exact observation it is necessary to fasten a surface of white 

 pa[)er behind the glass cylinder. 



Fix. 9. 



IV. 



In order to understand the forniation of jets it is advantageous, 

 first to learn the behavior of a definite quantity of liquid entering under 



