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a uniform or constant fact or principle. For specific named laws, see under the name.
law of independent assortment the members of gene pairs segregate independently during meiosis; see also mendel's laws.
inverse square law the intensity of radiation is inversely proportional to the square of the distance from the source of radiation.
law of segregation in each generation the ratio of (a) pure dominants, (b) dominants giving descendants in the proportion of three dominants to one recessive, and (c) pure recessives is 1:2:1. This ratio follows from the fact that the two alleles of a gene cannot be a part of a single gamete, but must segregate to different gametes. See also mendel's laws.


1. A principle or rule.
See also: principle, rule, theorem.
2. A statement of fact detailing a sequence or relation of phenomena that is invariable under given conditions.
See also: principle, rule, theorem.
[A.S. lagu]


(law) a uniform or constant fact or principle.
Allen's paradoxic law  the more sugar a normal person is given the more is utilized; the reverse is true in diabetics.
all-or-none law  see all or none.
Beer's law , Beer-Lambert law in spectrophotometry, the absorbance of a solution is proportional to the concentration of the absorbing solute and to the path length of the light beam through the solution.
Boyle's law  at a constant temperature the volume of a perfect gas varies inversely as the pressure, and the pressure varies inversely as the volume.
Charles' law  at a constant pressure the volume of a given mass of a perfect gas varies directly with the absolute temperature.
law of conservation of energy  in any given system the amount of energy is constant; energy is neither created nor destroyed, but only transformed from one form to another.
law of conservation of mass , law of conservation of matter mass (or matter) can be neither created nor destroyed; this law can be violated on the microscopic level.
Dalton's law  the pressure exerted by a mixture of nonreacting gases is equal to the sum of the partial pressures of the separate components; it holds true only at very low pressures.
Hellin's law , Hellin-Zeleny law one in about 89 pregnancies ends in the birth of twins; one in 89 × 89 (7921), of triplets; one in 89 × 89 × 89 (704,969), of quadruplets.
Henry's law  the solubility of a gas in a liquid solution at a constant temperature is proportional to the partial pressure of the gas above the solution.
law of independent assortment  genes that are not alleles are distributed to the gametes independently of one another; one of Mendel's laws.
Mendel's laws , mendelian laws two laws of inheritance of single-gene traits that form the basis of genetics; the law of segregation and the law of independent assortment.
Nysten's law  rigor mortis affects first the muscles of mastication, next those of the face and neck, then those of the trunk and arms, and last those of the legs and feet.
Ohm's law  the strength of an electric current varies directly as the electromotive force and inversely as the resistance.
Raoult's law  the vapor pressure of a volatile component of an ideal solution is equal to the mole fraction of that substance in solution times its vapor pressure in the pure state at the temperature of the solution; it is true only for ideal solutions and ideal gases.
law of segregation  the members of a pair of allelic genes segregate from one another and pass to different gametes; one of Mendel's laws.
law of similars  in homeopathy, the principle that a substance that in large doses will produce symptoms of a specific disease will, in extremely small doses, cure it.
laws of thermodynamics  Zeroth law: two systems in thermal equilibrium with a third are in thermal equilibrium with each other. First law: energy is conserved in any process. Second law: there is always an increase in entropy in any naturally occurring (spontaneous) process. Third law: absolute zero is unattainable.


Etymology: AS, lagu
1 (in a field of study) a rule, standard, or principle that states a fact or a relationship between factors, such as Dalton's law regarding partial pressures of gas or Koch's law regarding the specificity of a pathogen.
2 a rule, principle, or regulation established and promulgated by a government to protect or restrict the people affected; the field of study concerned with such laws; the collected body of the laws of a people, derived from custom and from legislation.
Government A regulation, statute, enactment, act, bill, decree, edict, bylaw, rule, ruling, ordinance, dictum, command, order, directive, pronouncement, proclamation, dictate, fiat
SciSpeak A uniform principle or constant


A uniform principle or constant. See Boyle's law, Charles' law, Farr's law of epidemics, Fick's law of diffusion, Frank-Starling law, Gown's law, Gresham's law, Hardy-Weinberg law, Harvard law, Heart law, Leborgne's law, Moore's law, Murphy's law of genetics, Natural law, Natural sexual law, Ohm's law, Periodic law, Roemer's law, Sutton's law, Talion law Government A legislative act that compels compliance. See AIDS disclosure law, Annie's law, Anti-dumping law, Antikickback law, Antisubstitution law, Antitrust law, Baby Doe law, Bad baby law, Chinese Law on Maternal & Infant Health Care law, Company doctor law, Due process law, Good Samaritan law, Heart law, Megan's law, Preemptive tobacco control law, Prompt payment law, Roemer's law, Seat belt law, Son of Sam law, Stark law, Sunset law.


1. A principle or rule.
2. A statement of a sequence or relation of phenomena that is invariable under the given conditions.
See also: principle, rule, theorem
[A.S. lagu]


principle or rule
  • Davis' law soft tissues' tendency to shorten and contract unless subject to frequent stretching

  • Hilton's law a joint and its motive muscles (+ insertions) are all supplied by the same nerve

  • Hook's law tissue strain (i.e. change in length) is directly proportional to applied compressive or stretching stress, so long as tissue elasticity (recoil ability) is not exceeded

  • inverse-square law radiation intensity is inversely proportional to square of distance from radiation source (rad = κ1/cm2)

  • law of excitation muscle tissue contracts in direct proportion to stimulating current strength

  • Newton's first law; law of inertia an object at rest will not move until acted upon by a force; an object in motion will remain in motion at constant velocity until acted on by a net force

  • Newton's second law; law of acceleration acceleration is directly proportional to applied force and indirectly proportional to object mass (i.e. force = mass × acceleration)

  • Newton's third law; law of reciprocal actions to every action there is an equal and opposite reaction; i.e. a body is maintained at rest by equal and opposing forces

  • Pascal's law a fluid at rest transmits pressure equally in every direction

  • Poiseuille's law vascular blood flow is inversely proportional to fourth power of vessel radius (i.e. the narrower the vessel, the greater the resistance to flow)

  • Starling's law the greater the stretch imposed on a circular muscle (e.g. muscle layer of an artery), the greater its reciprocal recoil and contraction

  • Wolff's law bone function changes cause bone structure modification (see bone modelling)


n 1. any rule within a legal system.
2. in science, a general principle describing an observed regularity.
3. a general organizing principle.
law of cure,
n in homeopathy, the pattern through which healing occurs. Specifically, from within to without, from top to bottom, from more serious to less serious, and in reverse order of development.
law of mother and child,
n in Chinese medicine, the natural order that dictates the association between the five elements—wood, metal, water, fire, and earth—to ensure harmony. Each element is believed to generate or “give birth” to another element in a cyclical pattern of wood-fire-earth-metal-water-wood. The interaction of these five elements serves as an example for familial behavior.
law of similars,
n in homeopathy, the principle governing the selection of a remedy. A substance that has been tested and shown to induce particular symptoms in a healthy person is administered to an individual suffering from those same symptoms to enhance the body's recovery mechanisms.
law, Arndt-Schulz, law that describes the link between the potency of a stimulus and its effectiveness on physiologic performance. Weak stimuli promote biologic life functions, moderate stimuli interfere with them, and strong stimuli reduce or annihilate them.
law, common,
n statutes created through a judge's decisions.
law, Head, according to which a painful stimulus, when applied to an area of low sensitivity which is bounded by an area of higher sensitivity, will be felt at the latter area rather than at the former.
law, Sherrington, 1. states that specific regions of the skin are innervated by specific posterior spinal nerve roots, although adjacent nerve fibers may also be present.
2. states that a contraction impulse to a muscle is paired with a relaxation impulse to that muscle's antagonist.
law, statute,
n ruling established by the governing authority.
laws, access to treatment,
n legislation that guarantees that patients have the right to obtain a procedure, device, or medication that is intended to be used as a mitigation, cure, therapeutic approach, or preventive measure.
laws, natural living, in naturopathic medicine, general principles that govern a healthy lifestyle, including eating foods that are natural and unrefined, exercising and resting for appropriate period of time, maintaining a moderately paced schedule, maintaining positive and stimulating emotional states, avoiding pollution and toxins, and properly eliminat-ing wastes from the body.


In science, a statement of facts or principles which is considered invariable under the given conditions having been tested and tried.
Abney's law The total luminance of an area is equal to the sum of the luminances that compose it.
Alexander's law An increase in the intensity of a jerk nystagmus when the eyes move in the direction of the fast phase.
all or none law The response in a nerve fibre to any stimulus strong enough to produce a response is always of the same amplitude. However, different nerve fibres have action potentials with different amplitudes. An increase in the intensity of the stimulus yields only an increase in the frequency of nerve impulses (or action potentials). Syn. all or nothing law.
Aubert-Förster law See Aubert-Förster phenomenon.
Bloch's law The luminance L of a stimulus required to produce a threshold response is inversely proportional to the duration of exposure t of the stimulus, i.e.
Lt = C
where C is a constant. This law is only valid for exposure t below about 0.1s.
Bunsen-Roscoe law In photochemistry, the product of the intensity of the light stimulus and the duration of exposure is a constant. Syn. law of reciprocity.
cosine law See diffusion.
Descartes' law See law of refraction.
Donders' law For any determinate position of the line of fixation with respect to the head there corresponds a definite and invariable angle of torsion.
Draper's law An effect is produced in a medium only by that portion of the spectrum which is absorbed by the medium. The effect may be thermal, chemical or the production of fluorescence. Syn. Grotthus' law.
Emmert's law The apparent size of a projected after-image varies in proportion to the distance of the surface on which it is projected. The law can be expressed by the following relationship h/H = d/D, where h is the linear size of the object, H the apparent size of the projected after-image, d the object's distance from the observer and D the distance between the observer and the surface on which the after-image is projected. It follows from the above expression that H = hD/d, i.e. the greater the distance of the projected image the larger its apparent size.l. of equal innervation See Hering's law of equal innervation.
Fechner's law The intensity of a sensation S varies as the logarithm of the intensity I of the stimulus, i.e.
S = k log I
where k is a constant. However, in some conditions this law is not valid and Stevens' law (or power law) is more appropriate. This stipulates that the intensity of a sensation S varies as the intensity of the stimulus I to the power of x, i.e.
S = kIx
where x is a constant which depends on the stimulus. See magnitude estimation.
Fermat's law The path taken by a light ray in going from one point to another is that route which takes the least time. Syn. Fermat's principle.
Ferry-Porter law The critical flicker frequency F is directly proportional to the logarithm of the luminance L of the stimulus, i.e.
F = a log L + b
where a and b are constants. See critical fusion frequency.
Granit-Harper law The critical fusion frequency increases with the logarithm of the retinal area stimulated.
Grassmann's law's Laws of colour mixture. 1. The first law states that any colour C of the visible spectrum can be matched in appearance by a mixture of three primary colours, such as red R, green G and blue B, provided that none of these can be matched by a mixture of the other two, i.e.
C = αR + βG + γB
where α, β and γ are the relative proportions of the chosen primaries.2. Additive property: if a colour is added in an identical manner to two equivalent mixtures (or single colours) the two new mixtures will appear identical, i.e. if A + B = C + D, then A + B + X = C + D + X, or if A = B, then A + X = B + X.3. Scalar property: if the brightness of each of two equivalent mixtures is increased or decreased by the same factor the two new mixtures will appear identical, i.e. if A + B = C + D, then k (A + B) = k (C + D).4. Associative property: if a colour is substituted in one of the mixtures by an equivalent colour the two new mixtures will appear identical, i.e. if A + B = C + D and X = B, then A + X = C + D.
Grotthus' law See Draper's law.
Helmholtz's law of magnification See Lagrange's law.
Hering's law of equal innervation Innervation to the extraocular muscles is equal to both eyes. Thus, all movements of the two eyes are equal and symmetrical. Syn. Hering's law; law of equal innervation. See yoke muscles.
law of identical visual directions An object stimulating corresponding retinal points is localized in the same apparent monocular direction in each eye. Syn. law of oculocentric visual direction. See line of direction; retinal corresponding points.
inverse square law of illumination The illuminance E of a surface by a point source is directly proportional to the luminous intensity I of a point source and to the cosine of the angle θ of incidence and inversely proportional to the square of the distance d between the surface and the source, i.e.
E = I cos (θ)/d2
Syn. law of illumination. See illuminance.
Imbert-Fick law Applied to applanation tonometry, this law states that the intraocular pressure P (in mmHg) is equal to the tonometer weight W (in g) divided by the applanated area A (in mm2), hence,
P = W/A
This law is correct only for infinitely thin, dry, elastic, spherical membranes.
Kirschmann's law The greatest contrast in colour is seen when the luminosity difference is small.
Knapp's law A correcting lens placed at the anterior focal plane of an axially ametropic eye forms an image equal in size to that formed in a standard emmetropic eye. Knapp's law applies to the relative spectacle magnification but not to the spectacle magnification. Syn. Knapp's rule.
Kollner's law See Kollner's rule.
Lagrange's law In paraxial optics, the product of the index of refraction of image space n′, the image size h′ and the half-angle of the refracted cone in image space u′ is equal to the product of the index of refraction of object space n, the object size h and the half-angle of the incident cone in object space u, i.e.
nhu′ = nhu
Syn. Helmholtz's law of magnification; Lagrange's relation; Smith-Helmholtz law. See sign convention.
Lambert's law See diffusion.
Listing's law 
When an eye moves to any position from the primary position, it may be considered to have made a single rotation about an axis that is perpendicular to both the initial and final lines of fixation at their point of intersection.
law of oculocentric visual direction See law of identical visual directions.
Piéron's law See Ricco's law.
Piper's law See Ricco's law.
Planck's law Law giving the energy distribution of a black body as a function of wavelength, for a specified temperature.
power law See Fechner's law.
Prentice's law The prismatic effect P in prism dioptres at a point on a lens is equal to the product of the distance c in centimetres of the point from the optical centre of the lens, and the dioptric power F of the lens, i.e.
P = cF
Syn. Prentice's rule. See differential prismatic effect; prism power; induced prism.
law of reciprocity See Bunsen-Roscoe law.
law of reflection The incident and reflected rays and the normal to the surface at the point of incidence lie in the same plane and the angle of incidence is equal to the angle of reflection (Fig. L5).
law of refraction The incident and refracted rays and the normal to the surface at the point of incidence lie in the same plane and the ratio of the sine of the angle of incidence i to the sine of the angle of refraction i′ is a constant for any two media, i.e.
where n and n′ are the refractive indices of the first and second medium, respectively. This constant (n′/n) is called the relative index of refraction for the two media. Syn. Descartes' law; Snell's law. See index of refraction; sign convention.
Ricco's law The product of the absolute threshold of luminance L and the image area A is a constant, i.e.
LA = C
This law is valid for small images subtending an angle of a few minutes of arc in the fovea and to one degree in the near macular region. For larger images in the macular area, Piéron's law applies; it states that the product of the luminance L of the image at threshold and the cube root of the retinal area A stimulated is a constant, i.e.
L3ÎA = C
In the peripheral retina, Piper's law becomes valid. This law states that the product of the luminance of the stimulus L and the square root of the area A is a constant, i.e.
In the far periphery of the retina, L tends to become independent of A.
Sherrington's law of reciprocal innervation The contraction of a muscle is accompanied by simultaneous and proportional relaxation of its antagonist. For example, if the superior oblique muscle contracts, its antagonist, the inferior oblique muscle, relaxes. The validity of this law has been established by electromyography.
Smith-Helmholtz law See Lagrange's law.
Snell's law See law of refraction.
Stevens' law See Fechner's law.
Talbot's law See Talbot-Plateau law.
Talbot-Plateau law The brightness of a light source presented at short intervals above the critical fusion frequency is equal to that which would be produced by a constant light source of an intensity equal to the mean value of the intermittent stimuli. Syn. Talbot's law.
Weber's law The just noticeable difference (or difference threshold) in intensity of a stimulus ΧI varies as a constant ratio of the initial intensity of the stimulus I, i.e.
ΧI = kI
where k = {ΧI/I} is a constant called Weber's fraction (Weber's constant). Example: if the initial stimulus was a light source of 1000 cd/m2 and k = 0.01 (or 1%), ΧI = 0.01 ✕ 1000 = 10 cd/m2. Syn. Weber-Fechner law. See differential threshold.
Weber-Fechner law See Weber's law.
Fig. L5 Light ray incident at O on a surface separating two media of different refractive indices, n and n ′enlarge picture
Fig. L5 Light ray incident at O on a surface separating two media of different refractive indices, n and n

Table L1 Approximate amount of spectacle lens decentration (in mm) of its optical centre away from the pupillary centre of the eye to produce five prismatic effects (in prism dioptres) for distance vision. The results ignore the effect of spherical aberration
lens power + or prismatic effect required
1 Χ2 Χ3 Χ4 Χ5 Χ
20 D0.
16 D0.
14 D0.
12 D0.
10 D1.
9 D1.
8 D1.
7 D1.
6 D1.
5 D2.
4 D2.55.07.510.012.5
3 D3.36.710.013.316.7
2 D5.
1 D10.


1. A principle or rule.
2. A statement of fact detailing a sequence or relation of phenomena that is invariable under given conditions.
[A.S. lagu]


n 1. that which is laid down or established. An enforceable rule of conduct. 2. that which must be obeyed and followed by citizens, subject to sanctions or legal consequences. The term is also used in opposition to fact. E.g., in a lawsuit, questions of law are to be decided by the court, whereas the jury decides questions in fact.
law, administrative,
n a set of specific rules and regulations overseen by an administrative agency in order to enforce the law.
law, case,
n the use of citations of previous court opinions in a court case, taken from the court decisions published by the state and federal government.
law, Charles's,
n the principle that states that all gases expand equally upon heating and contract equally upon cooling.
law, constitutional,
n the set of supreme laws set out in the U.S. Constitution. All other state and federal laws must be in accordance with the laws of the Constitution. The Constitution designates the roles of the three branches of government as well as setting forth which areas of law are in federal jurisdiction and which are left to the states.
law, Dalton's,
n the principle that states that the pressure of a mixture of gases equals the sum of the partial pressures of the constituent gases.
law, ignorance of,
n a want of knowledge or acquaintance with the laws of the land insofar as they apply to the act, relation, duty, or matter under consideration.
law, inverse-square,
n principle stating that the strength of radiation from a point source varies inversely as the square of the distance.
law, judicial,
n the interpretation of the written law by the courts. Decisions are often based on
stare decisis, the doctrine that allows the court to follow the decision made in a previous case in the same jurisdiction. A departure from the legal precedents is known as a landmark decision.
law, moral,
n the aggregate of rules and principles of ethics that relate to right and wrong conduct and prescribe the standards to which the actions of persons should conform in their dealings with each other.
law, neurologic,
n See law of specific energy.
law of radiosensitivity, BergonieTribondeau
(ber´gonē´ trebondō´), law stating that the resistance or sensitivity to radiation depends on the metabolic state of a cell, tissue, or an organ.
law of specific energy (neurologic law),
n principle that states, in essence, that sensory quality is perceived according to the nerve that is excited, not according to the object that excites. If pressure placed on the eyeballs stimulates the retina, light is perceived, not pressure; similarly, electrical stimulation will produce sensations of smell, taste, touch, or pain in accordance with the nerve stimulated but not a sensation of electricity as such. The special as well as the general senses maintain this principle.
law, tort,
n an area of law that deals with civil wrongs perpetrated against another person or private property. The primary concerns in dentistry are negligence and malpractice. A lapse in professional standards may be subject to proceedings for negligence or malpractice.
law, Wolff's,
n principle that states that all changes in the function of bone are attended by definite alterations in its internal structure.
law(s), written,
n/ the law or laws created by express legislation or enactment, as distinguished from
unwritten or
common law, which includes all law or laws from any other legal source.


1. natural law; a uniform or constant fact or principle in nature.
2. legal law; the laws of persons, developed so that social contacts between individuals can be managed on a basis of mutual understanding and agreement.

adversarial law (2) system
arguments are settled by having each opponent, one of whom is often the state, argue his/her case before a court, which decides the outcome, often on the basis of precedent in previous similar cases.
law (1) of the circle
the radiographic principle on which localization of a radioopaque foreign body can be specified exactly. It depends on taking the x-rays at right angles to each other, a ventrodorsal and a lateral.
civil law (2)
see inquisitorial law (below).
common law (2)
the law of common usage, in which principles are derived from case law and the judgments made in actual cases.
English law (2)
the original common law system.
law (1) of independent assortment
the members of gene pairs segregate independently during meiosis. See also mendel's laws.
inquisitorial law (2) system
the basis of Roman law. The court questions each of the adversaries in an argument and decides the outcome on the basis of the code layed down.
law (1) of mass action
the rate of a reversible reaction, in either direction, is proportional to the concentrations of the reacting substances.
private law (2)
law relating to the conduct of individuals, e.g. contract, divorce, matrimonial, property law.
public law (2)
the law relating to group conduct, especially the state and its criminal, industrial and constitutional law, but also corporation law.
Roman law (2)
law by application of an elaborate written code, the basis for most European law. It is an inquisitorial law system.
law (1) of segregation
in each generation the ratio of (1) pure dominants, (2) dominants giving descendants in the proportion of three dominants to one recessive, and (3) pure recessives is 1:2:1. This ratio follows from the fact that the two alleles of a gene cannot be a part of a single gamete, but must segregate to different gametes. See also mendel's laws.
law of Similars
the defining principle of homeopathy; substances that produce symptoms in disease can be used to treat diseases with those symptoms.
statute law (2)
that part of an English law system that is set down in statutes or law established by Act of Parliament of the day.

Starling's hypothesis, law

the law relating to the passage of fluid out of a capillary depending on the hydrostatic and osmotic pressures of the blood and the same pressures of tissue fluid, the net effect of the opposing pressures determining the direction and rate of flow.

Patient discussion about law

Q. Mother in law not accepting the diagnosis. Our 3 years old son was diagnosed with autism some time ago, and although it’s not easy, our family and friends support and help us a lot, except my mother in-law (that lives close to us). She refuse to accept the fact that our son has autism, and keeps telling we are just hysteric and with little education our child will grow up just fine. What can we do? Were we wrong when we decided to tell everyone?

A. I believe that it is a matter of time until your mother in-law realizes the full extent of your son's condition. Perhaps now she cannot accept it, and would rather think of him as a normal healthy child, and with time she will grow to understand his needs and capabilities. The most important thing for you to do is keep her involved in his life, so that she will give him all the love he can get from his grandmother, regardless of his autism. It seems to me you are a strong family with great people around you, that will help you with anything you need, so work on what is best for your son, and that is loving him. Don't spend too much time worrying about what others know or believe.

Q. My brother in law is dealing with cancer. how can I help my sister deal with him?? My brother in law's cancer is treated by the best doctors of the ccountry. what I'm afraid of is my sister's depression. Since her husband was diagnosed and stopped working she is so down, she can hardly take care of her kids.It's like her world has darkened and I really don't know how to help her. Would really appreciate any advice. thank you, bless you all.

A. I lost my husband to cancer 5yrs ago, and it really helped me alot when my friend would come and just sit with me, helped with my house work, phone calls, meals and just a hug now and again. Give her all the time she needs to talk and cry and allow her time to be afraid. It is all normal. Just keep loving her, she knows your there and will appreciate it. Even small things you do for her are now big. When you can make her smile do so..... My prayers are with all of you.

Q. My brother-in-law named Jacob has bi-polar schizophrenia; please help us by giving some solution for this… My brother-in-law named Jacob has bi-polar schizophrenia; he is currently on his medication and takes them faithfully in a positive mood. We have a hard time communicating with each other and it's destroying our marriage, please help us by giving some solution for this…

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