148 



THE MECHANICS OF THE EARTH'S ATMOSPHERE. 



The peculiar behavior of the origiually adhereut quiescent liquid, 

 whicli is afterward carried alonjj-, <'xplains the slow changes in the 

 jiathofthe current that is also observed with other solid bodies of 

 different shapes. 



If a jet strides upon a small brass sphere then with steady flow the 

 stream path gradually takes the form shown in Figs. 21, 22, 23, and 24. 



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Fis.21. 



Fii:. T2. 



We see how at first the sphere and the adherent liquid force the moviug 

 liquid to a deviation almost at right angles from its original course. 

 Then gradually the quiescent liquid is carried along, the stream sur- 

 lace follows the surface of the sphere continually more and more 

 closely. A consideration of the thin stream surface that finally en- 

 closes the greater part of the s[)here tempts one to assume that the 

 moving fluid glides along the surface of the sphere. At least, by means 

 of small solid bodies occasionally occurring in the liquid, one recognizes 

 that in the immediate neighborhood of the fixed obstacle the liquid 

 moves with finite velocity. 



The phenomena just described do not appear to depend especially on 

 the substance of the solid body, assuming of course that it is provided 

 with a smooth surface. Instead of the brass si)here an ivory sphere 

 may be used. This is in the same way gradually covered over with a 

 close-fitting stream surface. Similar to this was the process when the 

 jet struck against the lower end of a test tube. With a steady current 

 the lower part of the tube is slowly covered over with a thin stream 

 surface, which at a distance of about 4 centimetres from the lower end 

 of the glass surface bent away and ran into the spirals that here also 

 perpetually recur. 



Of further special interest is the case where the jet meets a definite 

 thin partition perpendicular to its own direction, since this current has 

 been theoretically treated by Kirchhoft' (Crelle's Journal, vol. lxx, p. 

 298), but under the rather different conditions already mentioned. 

 Therefore, a small circular plate was placed ])erpendicular to the jet. 

 The stream lines in this case depend essentially on tlie ratio of the 

 radii of the plate and the jet. If the radius of the circular plate is 



