It may immediately be asked--How is that public opinion to be
ascertained? The answer is--By ascertaining the _differences_ in
opinion between the present and the past. For this purpose it must be
observed, that the views of a past age are easily ascertainable, in
matters of law, from theoretical writings, history, and judicial
decisions; and these views may be reduced to definition. Modern
universal intelligence will either agree or disagree in these views.
In the mass of instances it will agree, as progress on such points is
at all times slow; and not only will the points of _disagreement_ be
few, but they will be salient, striking, and generally of popular
notoriety. Present, universal, or international opinion, has therefore
two portions. 1. That in which it accords with the views of a past
generation, that has become historical. 2. That in which it differs
from, or contradicts those views.

In the first instance, then, we are to ascertain what _were_ the
principles of right and justice, from any materials handed down to us;
and if those principles agree with, or support the practical rules
recorded by the same, or similar sources of information, such are to
be accepted as belonging to the code of the Laws of Nations, as far as
those principles are uncontradicted by modern opinion.

In the second instance, those differences which may either overrule,
add to, or complete the public opinion of a past age, are to be
ascertained, (by those in whose hands such decisions rest,) by looking
to the _wish_ of nations on these points; and this wish may be
exhibited in various ways; either by a universal abandonment of a
given law, in its non-execution by any nation whatever, for a length
of time; by numerous treaties, to obtain by convention an improvement
not yet declared by international tribunals; or by extending to the