ON FLOW OF SOLIDS UNDER GREAT PRESSURES. 
141 
A double orifice in the bottom, namely, two orifices of 
different sizes side by side, gave very interesting results ; the 
smaller orifice yielded a shorter jet, on account of the greater 
freedom of flow through the larger orifice, and the concentric 
layers of each jet were distorted towards the side facing the 
other jet, and drawn towards that side, as shown in the 
sections of the two jets in Fig. 6. 
Further, a centre large orifice was tried with six smaller 
orifices arranged round the centre one in the position of the 
six angles of a hexagon ; and the result was that instead of 
circular central jet, one of hexagonal character was obtained, 
having hollow grooved sides with projecting rounded angles 
towards each of the surrounding six holes, showing the 
disturbing effect of the simultaneous flow of material from 
the centre of the mass towards each of those six holes. 
The experiments that have been described were all made 
in closed cylinders, and the compressed material had con¬ 
sequently no means of escape except through the special 
orifice provided; and experiments were also tried in an open 
unconfined space, with a similar pile of lead discs compressed 
between two flat surfaces, as shown in Fig. 5, leaving the 
edges of the disc free to expand laterally. The middle discs 
of the whole pile flowed outwards the most freely, and became 
consequently the thinnest at their centre ; and the extreme 
top and bottom discs, being retarded in their flow by the 
friction against the compressing surfaces over which they had 
to flow, became curved and distorted in their form by the 
pressure of the other discs, this distortion gradually diminish¬ 
ing symmetrically towards the middle discs. 
The above experiments were then repeated with harder 
metals than lead, and it was found that with all of these, and 
even with steel itself, the same law of flowing under pressure 
applied, provided that the pressure was sufficiently increased 
in proportion to their hardness. 
I had the opportunity of witnessing some of Tresca’s 
experiments that have been described ; and the drawings from 
which the Figs, in Plate IY. have been copied I made direct 
from the several experimental pieces described; otherwise I 
should have hesitated to give full credence to the extraordinary 
results obtained. 
The special practical application that was made by Tresca 
of these results was in improvements in the modes of forging 
and working iron ; by so arranging the dies and tools that the 
metal was enabled to flow in a continuous solid stream during 
the process of changing its form under the hammer or press, 
so as to produce thoroughly sound work. It was known 
