138 
ON FLOW OF SOLIDS UNDER GREAT PRESSURES. 
2in. diameter that were forced through a hole only ^in. 
diameter, which made a continuous jet of as much as 23ft. 
length, consisting entirely of concentric tubes. 
In order to examine the process of the flow amongst the 
different particles of the lead, the ingenious plan was devised 
of making the original mass of lead in a series of thin flat 
discs, all of the same dimensions (like a pile of penny pieces), 
their touching surfaces being dusted with chalk to prevent 
the discs adhering together when under the severe pressure 
of the experiment, so that they could be taken apart again 
for examination at the close. The result was found to be 
that each of the original discs preserved its separate indivi¬ 
duality throughout the severe ordeal of forming the long jet; 
and the jet was found to be composed of a series of succes¬ 
sive layers or coats, each one fitting over the following one 
like a glove over a finger, and the whole showing a beauti¬ 
fully symmetrical figure when cut open longitudinally along 
the centre line of the jet. This is illustrated in Fig. 1 ; the 
successive layers being shown alternately black and white; 
and in Fig. 2 is shown a transverse section of the jet taken 
at the point A A in Fig. 1. 
When this process comes to be examined, it is seen that 
no other result could indeed have occurred, because a uniform 
force applied simultaneously to all the discs must produce a 
uniform result in all of them, and they have really no 
alternative but to follow one another regularly through the 
hole, as the only escape possible from the overpowering force 
that is urging them forward. 
Another form in which the experiment was tried was by 
1 laving a square hole in the side of the pressure cylinder at a 
little distance from the bottom, as shown in Fig. 7 ; instead 
of a round hole in the centre of the bottom, of the cylinder. 
The result found was that instead of a cylindrical jet being 
formed as before, consisting of a series of concentric 
envelopes, a square lateral jet was formed, composed of a 
series of flat horizontal layers of different lengths, overlap¬ 
ping one another; the discs directly opposite the orifice being- 
caused to flow out at once in a continuous flat ribbon, and 
the discs that were originally above the orifice then following 
on successively in the same course, as they became one after 
another brought down to the level of the orifice by the 
gradual compression of the whole mass. In Fig. 8 is shown 
a transverse section of the jet taken close to the orifice at 
the point B B in Fig. 7. 
An interesting point to notice is the behaviour of the 
different discs according to the position in which they hap- 
