\Mod"u*lus\, n.; pl. {Moduli}. [L., a small measure. See
{Module}, n.] (Math., Mech., & Physics)
A quantity or coefficient, or constant, which expresses the
measure of some specified force, property, or quality, as of
elasticity, strength, efficiency, etc.; a parameter.
{Modulus of a machine}, a formula expressing the work which a
   given machine can perform under the conditions involved in
   its construction; the relation between the work done upon
   a machine by the moving power, and that yielded at the
   working points, either constantly, if its motion be
   uniform, or in the interval of time which it occupies in
   passing from any given velocity to the same velocity
   again, if its motion be variable; -- called also the
   efficiency of the machine. --Mosley. --Rankine.
{Modulus of a system of logarithms} (Math.), a number by
   which all the Napierian logarithms must be multiplied to
   obtain the logarithms in another system.
{Modulus of elasticity}.
(a) The measure of the elastic force of any substance,
    expressed by the ratio of a stress on a given unit of the
    substance to the accompanying distortion, or strain.
(b) An expression of the force (usually in terms of the
    height in feet or weight in pounds of a column of the
    same body) which would be necessary to elongate a
    prismatic body of a transverse section equal to a given
    unit, as a square inch or foot, to double, or to compress
    it to half, its original length, were that degree of
    elongation or compression possible, or within the limits
    of elasticity; -- called also {Young's modulus}.
{Modulus of rupture}, the measure of the force necessary to
   break a given substance across, as a beam, expressed by
   eighteen times the load which is required to break a bar
   of one inch square, supported flatwise at two points one
   foot apart, and loaded in the middle between the points of
   support. --Rankine.