DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Law-of-the-Wall Scaling Relations
Length LLs ∼ z
Time τLs ∼ zu ∗ −1
Velocity wLs ∼ u ∗
Dissipation of turbulent kinetic energy εLs ∼ u∗ 3 (κz) −1
Temperature (fluctuations) Ls ∼ Fth/(ρcpu ∗ )
found by Friedmann (see Friedmann–Lemaître
cosmological models) and several contributions
to relativistic cosmology based on these models.
His other achievements include the theory
of “primaeval atom” — an overall vision
of the origin and evolution of the universe (now
replaced by the more detailed and better confirmed
observationally Big Bang theory), several
papers on physics of cosmic rays (which he
interpreted as remnants of what is now called the
Big Bang), mathematical physics, celestial mechanics,
and automated computing (even before
electronic computers were invented).
Lemaître–Tolman cosmological model Inhomogeneous
cosmological model first described
in 1933 by G. Lemaître, but now commonly
called the Tolman model. See Tolman
model.
lengthofday Thelengthofday hasdecreased
with geological time. The rotational period of
the Earth has slowed due to tidal dissipation.
lens A transparent solid through which light
can pass, and which has engineered-in propertiestodeflectorfocusthelight.
Seegravitational
lens.
Lense–Thirring precession The dragging of
space and time by a rotating mass, most evident
in cases of rapidly rotating compact objects,
such as Kerr black holes. Predicted using
the equations of general relativity by J. Lense
and H. Thirring in 1918, the effect has been
presumably detected by the extremely tiny effects
on satellites orbiting Earth, and around
distant, rotating objects with very intense gravitational
field, such as neutron stars and black
holes. The Lense–Thirring effect gives rise to
a precessional motion if an object is not orbiting
in the equatorial plane of the massive body.
© 2001 by CRC Press LLC
Lewis number
In the vicinity of a rotating black hole, within
the ergosphere, the dragging is strong enough to
force all matter to orbit in the equatorial plane
of the black hole. See accretion disk, Kerr black
hole.
lepton A fundamental spin 1/2 fermion that
does not participate in strong interactions. The
electrically charged leptons are the electron, the
muon, the tau, and their antiparticles. Electrically
neutral leptons are called neutrinos and
have very small (or zero) mass. The neutrinos
are observed to have only one helicity state
(left-handed). Their antiparticles have positive
helicity.
leveling (survey) A geodetic measurement
to obtain height difference between two points.
The height difference between the two points
can be obtained by erecting leveling rods at two
distant points from several to tens of several
meters, and then by reading scales of the leveling
rods using a level that is placed horizontally
at the intermediate distance between the
two points. Repeating this operation, height difference
between substantially distant two points
can be measured. Height above the sea at a
point can be obtained from control points whose
height above the sea has already been determined
(bench marks) or from height difference
between the point and tide gage stations. This
kind of leveling is referred to as direct leveling,
whereas trigonometric leveling and barometric
leveling are called indirect leveling.
Lewis number The non-dimensional ratio
LC = DC/DT, where DC is molecular diffusivity
of substance C and DT is molecular diffusivity
of heat, expresses the ratio of the rate of
transfer of molecules of C to that of heat. LC
in water is strongly temperature-dependent and
of the order of 0.01. The turbulent Lewis num-
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