314 PHENOMENA OF SUCTION. 



escaping current, but the ultimate effect is th.it 

 pressure over the greater portion of the space oetween 

 discs is less than the external pressure of the atm 

 phere : hence the remarkable result that the exte 

 air presses the suspended disc against the currer 

 blown from the tube and moves it close to the fixe 

 disc, and not until the curren" of air diminishes i 

 strength will the disc fall back again. 



A similar expansion of a current of air, which floT\ 

 from an aperture under a pressure sorr.ewhac great( 

 than that of the external air is always observed, eve 

 if the issuing current is not made to spread out in ar 

 definite manner as it is in the last experiment, 

 liquid which issues from an orifice, forms a jet of near 

 uniform thickness ; but a gas blown through a tw 

 forms, in expanding, a cone; as can be well seen 

 the case of smoke or steam. The particles move : 

 first in straight lines forwards, but being at first dens' 

 than the external air they become gradually less den 1 

 by expansion, and move away from one another sic- 

 ways, and this lateral motion continues as long as t j 

 pressure is unequal. But in consequence of the iner i 

 of the moving particles the lateral motion contim| 

 even a short time after the pressure is equalised, a I 

 the issuing gas becomes less dense than atmosphe 

 air, and consequently its pressure also becomes sonf 

 what less. The resistance of the external air, exert h 

 principally in front of the issuing current, soon resto :. 

 in the latter the atmospheric pressure, but at a s] it 

 near to the orifice, a diminished pressure may be actuaiy 

 observed: at this spot air enters from the sides, mL > 

 with the issuing current, and is carried onwards with 



