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  joule \joule\ (j[=oo]l), n. [From the distinguished English
     physicist, James Prescott Joule (1818-1889).] (Physics.)
     A unit of work which is equal to 10^{7 ergs (the unit of
     work in the C. G. S. system of units), and is equivalent to
     one watt-second, the energy expended in one second by an
     electric current of one ampere in a resistance of one ohm;
     also called the absolute joule. It is abbreviated J or j.
     The international joule is slightly larger, being 1.000167
     times the absolute joule. The absolute joule is approximately
     equal to 0.737562 foot pounds, 0.239006 gram-calories (small
     calories), and 3.72506 x 10^{-7 horsepower-hours, and
     0.000948451 B.t.u. --HCP61
     [1913 Webster +PJC]
  
     Joule's equivalent. See under Equivalent, n.
        [1913 Webster]

  Equivalent \E*quiv"a*lent\ ([-e]*kw[i^]v"[.a]*lent), n.
     1. Something equivalent; that which is equal in value, worth,
        weight, or force; as, to offer an equivalent for damage
        done.
        [1913 Webster]
  
              He owned that, if the Test Act were repealed, the
              Protestants were entitled to some equivalent. . . .
              During some weeks the word equivalent, then lately
              imported from France, was in the mouths of all the
              coffeehouse orators.                  --Macaulay.
        [1913 Webster]
  
     2. (Chem.) That comparative quantity by weight of an element
        which possesses the same chemical value as other elements,
        as determined by actual experiment and reference to the
        same standard. Specifically:
        (a) The comparative proportions by which one element
            replaces another in any particular compound; thus, as
            zinc replaces hydrogen in hydrochloric acid, their
            equivalents are 32.5 and 1.
        (b) The combining proportion by weight of a substance, or
            the number expressing this proportion, in any
            particular compound; as, the equivalents of hydrogen
            and oxygen in water are respectively 1 and 8, and in
            hydric dioxide 1 and 16.
            [1913 Webster]
  
     Note: This term was adopted by Wollaston to avoid using the
           conjectural expression atomic weight, with which,
           however, for a time it was practically synonymous. The
           attempt to limit the term to the meaning of a
           universally comparative combining weight failed,
           because of the possibility of several compounds of the
           substances by reason of the variation in combining
           power which most elements exhibit. The equivalent was
           really identical with, or a multiple of submultiple of,
           the atomic weight.
           [1913 Webster]
  
     3. (Chem.) A combining unit, whether an atom, a radical, or a
        molecule; as, in acid salt two or more equivalents of acid
        unite with one or more equivalents of base.
        [1913 Webster]
  
     Mechanical equivalent of heat (Physics), originally defined
        as the number of units of work which the unit of heat can
        perform, equivalent to the mechanical energy which must be
        expended to raise the temperature of a pound of water one
        degree Fahrenheit; later this value was defined as one
        British thermal unit (B.t.u). Its value was found by
        Joule to be 772 foot pounds; later measurements give the
        value as 777.65 foot-pounds, equivalent to 107.5
        kg-meters. This value was originally called Joule's
        equivalent, but the modern Joule is defined differently,
        being 10^{7 ergs. The B.t.u. is now given as 1,054.35
        absolute Joules, and therefore 1 calorie (the amount of
        heat needed to raise one gram of water one degree
        centigrade) is equivalent to 4.186 Joules.
        [1913 Webster + PJC]
  
     Note: The original definition of the Mechanical equivalent of
           heat in the 1913 Webster was as below. The difference
           between foot pounds and kilogram-meters ("on the
           centigrade scale") is puzzling as it should be a factor
           of 7.23, and the figure given for kilogram-meters may
           be a mistaken misinterpretation of the report. -- PJC:
           The number of units of work which the unit of heat can
           perform; the mechanical energy which must be expended
           to raise the temperature of a unit weight of water from
           0[deg] C. to 1[deg] C., or from 32[deg] F. to 33[deg]
           F. The term was introduced by Dr. Mayer of Heilbronn.
           Its value was found by Joule to be 1390 foot pounds
           upon the Centigrade, or 772 foot pounds upon the
           Fahrenheit, thermometric scale, whence it is often
           called Joule's equivalent, and represented by the
           symbol J. This is equal to 424 kilogram meters
           (Centigrade scale). A more recent determination by
           Professor Rowland gives the value 426.9 kilogram
           meters, for the latitude of Baltimore.
           [1913 Webster +PJC]

  Joule \Joule\ (j[=oo]l), n. [From the distinguished English
     physicist, James P. Joule.] (Physics.)
     A unit of work which is equal to 10^{7 units of work in the
     C. G. S. system of units (ergs), and is practically
     equivalent to the energy expended in one second by an
     electric current of one ampere in a resistance of one ohm.
     One joule is approximately equal to 0.738 foot pounds.
  
     Joule's equivalent. See under Equivalent, n.

  
  
     Note: This term was adopted by Wollaston to avoid using the
           conjectural expression atomic weight, with which,
           however, for a time it was practically synonymous. The
           attempt to limit the term to the meaning of a
           universally comparative combining weight failed,
           because of the possibility of several compounds of the
           substances by reason of the variation in combining
           power which most elements exhibit. The equivalent was
           really identical with, or a multiple of submultiple of,
           the atomic weight.
  
     3. (Chem.) A combining unit, whether an atom, a radical, or a
        molecule; as, in acid salt two or more equivalents of acid
        unite with one or more equivalents of base.
  
     Mechanical equivalent of heat (Physics), the number of
        units of work which the unit of heat can perform; the
        mechanical energy which must be expended to raise the
        temperature of a unit weight of water from 0[deg] C. to
        1[deg] C., or from 32[deg] F. to 33[deg] F. The term was
        introduced by Dr. Mayer of Heilbronn. Its value was found
        by Joule to be 1390 foot pounds upon the Centigrade, or
        772 foot pounds upon the Fahrenheit, thermometric scale,
        whence it is often called Joule's equivalent, and
        represented by the symbol J. This is equal to 424 kilogram
        meters (Centigrade scale). A more recent determination by
        Professor Rowland gives the value 426.9 kilogram meters,
        for the latitude of Baltimore.