446 
NATURE 
[SEPTEMBER 7, 1899 
strains had been pre-eminent, has probably been the initiative 
cause of an acute epoch of crust torsion and folding along oblique 
and transverse lines. 
The new movements affected all European areas, dovetailing 
new folds into the midst of, and across, old folds, and determin- 
ing new centres of virgation. In the Alps new arches and 
troughs were formed obliquely and transversely across the older 
series; the first-formed basins in the 
themselves over-arched or blocked up as the fan-shaped mountain- 
massives gradually became more and more compactly pressed 
middle than near either bank. If we could look beneath the 
surface and see what was going on there, we should find that 
the velocity was not so great near the bottom as at the top, and 
was scarcely the same at any two points of the depth. The 
more we study the matter, the more complex the motion appears 
to be; small floating bodies are not only carried down at dif- 
| ferent speeds and across each other’s paths, but are whirled 
new movement were | 
together, and the great torsion-basins of southern Europe | 
became ccnfirmed in their new shape and position acquired in 
accordance with the altered conditions of crust equilibrium. 
As might be expected, there is frequent indication that 
eruptive activily in Tertiary time broke out afresh in the same 
areas where eruptive activity had marked the Upper Carboniferous 
and Permo-Triassic period of movements. But the chief groups 
of eruptive rock round the inner caves of the Alps, Apennines 
and Carpathians, as well as the injections along oblique directions 
of shearing, may be clearly identified with the Tertiary torsion 
movements, for the most part, with the acute Mid-Tertiary 
epoch of torsion. 
Fic. 2. 
central massives may belong in part to the ancient Paleozoic or 
Permo-Carboniferous epochs of upheaval, in part to the late- 
Mesozoic and Tertiary epochs. 
A general conclusion may be made from the above that there 
are serpentines, diorites, granites, felsites, basalts in Alpine 
folds and faults which can be identified more especially with 
the ‘‘evolute” phenomena of Tertiary torsional movements. 
And these intrusions, injections, and eruptions involved in the 
last acute epoch of upheaval in Southern Europe are clearly 
correlated with similar eruptive phenomena throughout the same 
period in other parts of Europe, e.g. Auvergne, Scotland, 
Iceland. MariA M. OGILVIE. 
THE MOTION OF A PERFECT LIQUID} 
[F we look across the surface of a river, we cannot fail to 
observe the difference of the movement at various points. 
Near one bank the velocity may be much less than near the 
‘ther, and generally, though not always, it is greater in the 
urse delivered at the Royal Institution on Friday, February 10, 
by Prof. H. S. Hele-Shaw. 
NO. 1558, VOL. 60] 
round and round in small whirlpools, sometimes even disappear- 
ing for a time beneath the surface. By watching floating 
bodies we can sometimes realise these complex movements, but 
they may take place without giving the slightest evidence of 
their existence. 
You are now looking at water flowing through a channel of 
varying cross section, but there is very little evidence of any dis- 
turbance taking place. By admitting colour, although its effect 
is at ence visible on the water, it does not help us much to 
understand the character of the flow. If, however, fine bubbles 
of air areadmitted, we at once perceive (Fig. 1) the tumultuous 
conditions under which the water is moving and that there is a 
strong whirlpool action. This may be intensified by closing in 
two sides (Fig. 2), so as to imitate the action of a sluice gate, 
The larger masses of ignecus rocks in the | through the narrow opening of which the water has all to pass, 
the presence of air making the disturbed behaviour of the water 
very evident. 
Now you will readily admit that it is hopeless to begin to 
study the flow of the water under such conditions, and we 
naturally ask, are there not cases in which the action is more 
simple? Such would be the case if the water flowed very 
slowly in a perfectly smooth and parallel river bed, when the 
particles would follow one another in lines called ‘‘stream- 
lines,” and the flow would be like the march of a disciplined 
army, instead of like the movement of a disorderly crowd, in 
which free fights taking place at various points may be supposed 
to resemble the local disturbances of whirlpools or vortices. 
The model (Fig. 3) represents on a large scale a section of the 
channel already shown, in which groups of particles of the 
water are indicated by round balls, lines in the direction of flow 
of these groups (which for convenience we may call particles) 
being coloured alternately. When I move these so that the 
lines are maintained, we imitate ‘‘stream-line” motion, and 
when, at any given point of the pipe, the succeeding particles 
always move at exactly the same velocity, we have what is 
understood as ‘‘ steady motion.” 
