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town (1990 pop. 40,023), McLean co., central Ill.; inc. 1865. It is the center of a productive farming region. Motor vehicles are manufactured in Normal. The town originally grew around Illinois State Univ. (1857; formerly called Illinois State Normal Univ.), which remains a major contributor to its economy.



(to a curve or surface). The normal at a given point of a curve or surface is a line that passes through this point and is perpendicular to the tangent line or tangent plane at the same point of the curve or surface. A plane curve has at each point a single normal that lies in the plane of the curve. If x = f(t) and y = g(t) are parametric equations of a plane curve L, then the equation of the normal at point (x0, y0) of curve L that corresponds to the value to of the parameter; may be written as

For a plane curve defined by the equation F(x,y) = 0, the equation of the normal has the form

A space curve has at each point an infinite set of normals, and these normals all lie in a certain plane (the normal plane). The normal that lies in the osculating plane is called the principal normal. The normal that is perpendicular to the osculating plane is called the binormal. The tangent, the principal normal, and the binormal form the moving trihedral of the curve.

For the surface defined by the equation F(x, y, z) = 0, the normal can be represented by the equations

The concept of the normal plays a significant role not only in differential geometry but also in various applications of this subject, such as geometrical optics and mechanics. The formulation of the fundamental laws of refraction and reflection of light rays is an example from geometrical optics; in mechanics, a mass point or a physical body experiences a reaction directed along the normal when it is displaced along smooth curves or surfaces; in a conservative field, the lines of force at each point are directed along the normal to the isopotential surface that passes through the point.


The average value of a meteorological element over any fixed period of years that is recognized as standard for the country and element concerned.


i. As it pertains to meteorology, the value of an element averaged for a given location over a period of time, normally fifty years, and recognized as a standard.
ii. Equivalent to usual, regular, rational, or standard conditions.
iii. At a right angle to the datum under reference.


1. Psychol
a. being within certain limits of intelligence, educational success or ability, etc.
b. conforming to the conventions of one's group
2. Biology Med (of laboratory animals) maintained in a natural state for purposes of comparison with animals treated with drugs, etc.
3. Chem (of a solution) containing a number of grams equal to the equivalent weight of the solute in each litre of solvent.
4. Chem denoting a straight-chain hydrocarbon: a normal alkane. Prefix: n-, e.g. n-octane
5. Geometry another word for perpendicular
6. Geometry a line or plane perpendicular to another line or plane or to the tangent of a curved line or plane at the point of contact
References in periodicals archive ?
It is also easy to see that there is no normal concentration of measure in the sense of (4.
For two bottles containing normal concentrations of toxic metals, the concentration of arsenic is not certified and a reference value of 60 [micro]g/L has been provided for information.
6 percent of those whose blood sugar was kept near normal concentrations.
3] concentrations along with normal concentrations of TSH are typical, unless the patient had previous successful surgery or radioactive iodine therapy.
This brain chemical is similar to mood-elevating amphetamines and is found in lower than normal concentrations in individuals suffering from depression and bipolar disorder.
The system also reduces airborne particulates and pathogens in enclosed areas with normal concentrations of substances such as dust, pollen and bacteria.
In all cases zinc oxide at lower than normal concentrations produces the best fatigue resistance.
In this population of men that previously used a topical testosterone, after three months of treatment, no men on testosterone or placebo exhibited normal concentrations for both measures.
PATIENTS AND METHODS: The study population consisted of 282 men aged 36 to 85 years old with normal concentrations of total testosterone.
In this population of men that previously used a topical testosterone, no men on testosterone or placebo exhibited normal concentrations for both measures.
4] were dissolved in normal human serum ultrafiltrate, void of serum proteins, containing normal concentrations of serum electrolytes and free thyroid hormones.
A possible explanation for the differences in the effects of chlordane is that for the embryos irreversibly differentiated as males, lower testosterone concentrations elicit an increase in reductase activity, so that late-stage embryos and hatchlings have normal concentrations of nonaromatizable androgens.