PAPER BY PROF. OBERBECK. 



145 



We can now i)as.s on to the foiuiatiou of jets proper by steady 

 currents. If we allow the stop-cock to be open for a loii<i' time thei-e 

 arises (at first rapidly, afterward slowly) a jet whose upi)er ])ortion has 

 great similarity with the forms hitherto described. TL'.e jet soon attains 

 a certain altitude that depends upon the difference of pressure and 

 above which it does not ordinarily go, or at least only with extreme 

 slowness. Thus for a difierence of pressure of 5 millimetres the alti- 

 tude of the jet is about 20 millimetres; for 10 millimetres pressure 

 the altitude is about 80 milliir.etres; for 20 millimetres pressure the 



altitude is 200 millimetres; and 



for 30 millimetres diiferenee of 



pressure the jet attains the upper 



limit of the water at an altitude 



of about 400 millimetres in about 



80 seconds. The colored liquid 



spreads out over the surface of 



the colorless water and thence 



diffuses very slowly downward. 



The above given numbers do not 



])resent any general law, but only 



give approxiaiatelv the connec- 

 tion between the altitude of the 



jet and the difference of pressure. 



The former also depends some- 

 what on the specific gravity of 



the inflowing liquid, which varies 



a little with the quantity of added 

 Fig. lu. coloring material. It depends 



also on the size of the discharg- 

 ing aperture. Moreover the form of the front part of the jet is not 

 always exactly the same; in the figs. 10 and 17 are given two of the 

 ordinary forms of jet. In both these forms the jets proper are the 

 same; the bell-shaped expansion, however, is formed in a somewhat 

 different manner, perhaps conditioned by small variations of tempera- 

 ture in the colorless liquid. 



By the avoidance of all disturbances the jets here described remain 

 many minutes entirely unchanged. Only the bell-shaped portion con- 

 tinues to extend slowly somewhat further downwards. Moreover, with 

 respect to small disturbances the jets showed themselves by no means 

 very sensitive. If by a gentle pressure on the India-rubber tube the 

 velocity of the discharging liquid is diminished for au instant, then 

 water presses from all sides into the jet; after the cessation of this 

 pressure the origiual form of the jet is immediately resumed. Even 

 SO A 10 



1< ig. 17. 



