Chapter VI: Marine Insurance (4)

If the glasses be in contact, as is usually supposed in the theory of
Newton's rings, [alpha] = 0, and [delta]x[oo][lambda]^(1/2), or the
width of the band of the n^(th) order varies as the square root of the
wave-length, instead of as the first power. Even in this case the
overlapping and subsequent obliteration of the bands is greatly
retarded by the use of the prism, but the full development of the
phenomenon requires that [alpha] should be finite. Let us inquire what
is the condition in order that the width of the band of the n^(th)
order may be stationary, as [lambda] varies. By (14) it is necessary
that the variation of [lambda]^2/((1/2)n[lambda] - [alpha]) should
vanish. Hence a = (1/4)n[lambda], so that the interval between the
surfaces at the place where the n^(th) band is formed should be half
due to curvature and half to imperfect contact at the place of closest
approach. If this condition be satisfied, the achromatism of the
n^(th) band, effected by the prism, carries with it the achromatism of
a large number of neighbouring bands, and thus gives rise to the
remarkable effects described by Newton. Further developments are
given by Lord Rayleigh in a paper "On Achromatic Interference Bands"
(_Phil. Mag._, 1889, 28, pp. 77, 189); see also E. Mascart, _Traite
d'optique_.

In Newton's rings the variable element is the thickness of the plate,
to which the retardation is directly proportional, and in the ideal
case the angle of incidence is constant. To observe them the eye is
focused upon the thin plate itself, and if the plate is very thin no
particular precautions are necessary. As the plate thickens and the
order of interference increases, there is more and more demand for
homogeneity in the light, and we may have recourse to a sodium-flame
or a helium vacuum tube. At the same time the disturbing influence of
obliquity increases. Unless the aperture of the eye is reduced, the
rays reaching it from even the same point of the plate are differently
affected, and complications ensue tending to impair the distinctness
of the bands. To obviate this disturbance it is best to work at
incidences as nearly as possible perpendicular.

The bands seen when light from a soda flame falls upon nearly parallel
surfaces are often employed as a test of flatness. Two flat surfaces
can be made to fit, and then the bands are few and broad, if not
entirely absent; and, however the surfaces may be presented to one
another, the bands should be straight, parallel and equidistant. If
this condition be violated, one or other of the surfaces deviates from
flatness. In fig. 4, A and B represent the glasses to be tested, and C
is a lens of 2 or 3 ft. focal length. Rays diverging from a soda flame
at E are rendered parallel by the lens, and after reflection from the
surfaces are recombined by the lens at E. To make an observation, the
coincidence of the radiant point and its image must be somewhat
disturbed, the one being displaced to a position a little beyond, and
the other to a position a little in front of the diagram. The eye,
protected from the flame by a suitable screen, is placed at the image,
and being focused upon AB, sees the field traversed by bands. The
reflector D is introduced as a matter of convenience to make the line
of vision horizontal.

These bands may be photographed. The lens of the camera takes the
place of the eye, and should be as close to the flame as possible.
With suitable plates, sensitized by cyanin, the exposure required may
vary from ten minutes to an hour. To get the best results, the hinder
surface of A should be blackened, and the front surface of B should be
thrown out of action by the superposition of a wedge-shaped plate of
glass, the intervening space being filled with oil of turpentine or
other fluid having nearly the same refraction as glass. Moreover, the
light should be purified from blue rays by a trough containing
solution of bichromate of potash. With these precautions the dark
parts of the bands are very black, and the exposure may be prolonged
much beyond what would otherwise be admissible.

By this method it is easy to compare one flat with another, and thus,
if the first be known to be free from error, to determine the errors
of the second. But how are we to obtain and verify a standard? The
plan usually followed is to bring _three_ surfaces into comparison.
The fact that two surfaces can be made to fit another in all azimuths
proves that they are spherical and of equal curvatures, but one convex
and the other concave, the case of perfect flatness not being
excluded. If A and B fit one another, and also A and C, it follows
that B and C must be similar. Hence, if B and C also fit one another,
all three surfaces must be flat. By an extension of this process the
errors of three surfaces which are not flat can be found from a
consideration of the interference bands which they present when
combined in three pairs.

The free surface of undisturbed water is almost ideally flat, and, as
Lord Rayleigh (_Nature_, 1893, 48, 212) has shown, there is no great
difficulty in using it as a standard of comparison. Following the same
idea we may construct a parallel plate by superposing a layer of water
upon mercury. If desired, the superior reflecting power of the mercury
may be compensated by the addition of colouring matter to the water.

_Haidinger's Rings dependent on Obliquity._--It is remarkable that the well-known theoretical investigation, undertaken with the view of explaining Newton's rings, applies more directly to a different system of rings discovered at a later date.

The results embodied in equations (1) to (8) have application in the
first instance to plates whose surfaces are absolutely parallel,
though doubtless they may be employed with fair accuracy when the
thickness varies but slowly.

We have now to consider t constant and [alpha]' variable in (1). If
[alpha]' be small,

[delta] = 2[mu]t(1 - (1/2)[alpha]'^2) = 2[mu]t - t[alpha]^2/[mu] (15);

and since the differences of [delta] are proportional to [alpha]^2,
the law of formation is the same as for Newton's rings, where [alpha]'
is constant and t proportional to the square of the distance from the
point of contact. In order to see these rings distinctly the eye must
be focused, not upon the plate, but for infinitely distant objects.

The earliest observation of rings dependent upon obliquity appears to have been made by W. von Haidinger (_Pogg. Ann._, 1849, 77, p. 219; 1855, 96, p. 453), who employed sodium light reflected from a plate of mica (e.g. 0.2 mm. thick). The transmitted rays are the easier to see in their completeness, though they are necessarily somewhat faint. For this purpose it is sufficient to look through the mica, held close to the eye and perpendicular to the line of vision, at a sheet of white paper or card illuminated by a sodium flame. Although Haidinger omitted to consider the double refraction of the mica and gave formulae not quite correct for even singly refracting plates, he fully appreciated the distinctive character of the rings, contrasting _Beruhrungsringe und Plattenringe_. The latter may appropriately be named after him. Their tardy discovery may be attributed to the technical difficulty of obtaining sufficiently parallel plates, unless it be by the use of mica or by the device of pouring water upon mercury. Haidinger's rings were rediscovered by O. R. Lummer (_Wied. Ann._, 1884, 23, p. 49), who pointed out the advantages they offer in the examination of plates intended to be parallel.

The illumination depends upon the intensity of the monochromatic
source of light, and upon the reflecting power of the surfaces. If R
be the intensity of the reflected light we have from (7)

1 (1 - e^2)^2
--- = 1 + --------------------------------;
R 4e^2 sin^2 ((1/2)[kappa][delta])

from which we see that if e = 1 absolutely, 1/R = R = 1 for all values
of [delta]. If e = 1 very nearly, R = 1 nearly for all values of
[delta] for which sin^2((1/2)[kappa][delta]) is not very small. In the
light reflected from an extended source, the ground will be of full
brightness corresponding to the source, but it will be traversed by
_narrow_ dark lines. By transmitted light the ground, corresponding to
general values of the obliquity, will be dark, but will be interrupted
by narrow bright rings, whose position is determined by sin
(1/2)([kappa][delta]) = 0. In permitting for certain directions a
complete transmission in spite of a high reflecting power (e) of the
surfaces, the plate acts the part of a resonator.

There is no transparent material for which, unless at high obliquity,
e approaches unity. In C. Fabry and A. Perot's apparatus the
reflections at nearly perpendicular incidence are enhanced by lightly
silvering the surfaces. In this way the advantage of narrowing the
bright rings is attained in great measure without too heavy a
sacrifice of light. The plate in the optical sense is one of air, and
is bounded by plates of glass whose inner silvered surfaces are
accurately flat and parallel. The outer surfaces need only ordinary
flatness, and it is best that they be not quite parallel to the inner
ones. The arrangement constitutes a _spectroscope_, inasmuch as it
allows the structure of a complex spectrum line to be directly
observed. If, for example, we look at a sodium flame, we see in
general two distinct systems of narrow bright circles corresponding to
the two D-lines. With particular values of the thickness of the plate
of air the two systems may coincide so as to be seen as a single
system, but a slight alteration of thickness will cause a separation.

It will be seen that in this apparatus the optical parts are
themselves of extreme simplicity; but they require accuracy of
construction and adjustment, and the demand in these respects is the
more severe the further the ideal is pursued of narrowing the rings by
increase of reflecting power. Two forms of mounting are employed. In
one instrument, called the _interferometer_, the distance between the
surfaces--the thickness of the plate--is adjustable over a wide range.
In its complete development this instrument is elaborate and costly.
The actual measurements of wave-lengths by Fabry and Perot were for
the most part effected by another form of instrument called an
_etalon_ or interference-gauge. The thickness of the optical plate is
here fixed; the glasses are held up to metal knobs, acting as
distance-pieces, by adjustable springs, and the final adjustment to
parallelism is effected by regulating the pressure exerted by these
springs. The distance between the surfaces may be 5 or 10 mm.

The theory of the comparison of wave-lengths by means of this
apparatus is very simple, and it may be well to give it, following
closely the statement of Fabry and Perot (_Ann. chim. phys._, 1902,
25, p. 110). Consider first the cadmium radiation [lambda] treated as
a standard. It gives a system of rings. Let P be the ordinal number of
one of these rings, for example the first counting from the centre.
This integer is supposed known. The order of interference at the
centre will be p = P + [epsilon]. We have to determine this number
[epsilon], lying ordinarily between 0 and 1. The diameter of the ring
under consideration increases with [epsilon]; so that a measure of
the diameter allows us to determine the latter. Let t be the thickness
of the plate of air. The order of interference at the centre is p =
2t/[lambda]. This corresponds to normal passage. At an obliquity i the
order of interference is p cos i. Thus if x be the angular diameter of
the ring P, p cos (1/2)x = P; or since x is small,

p = P(1 + (1/8)x^2).

In like manner, from observations upon another radiation [lambda]' to
be compared with [lambda], we have

p' = P'(1 + (1/8)x'^2);

whence if t be treated as an absolute constant,

[lambda]' P / x^2 x'^2 \
--------- = --- ( 1 + --- - ---- ) (16).
[lambda] P' \ 8 8 /

The ratio [lambda]/[lambda]' is thus determined as a function of the
angular diameters x, x' and of the integers P, P'. If P, say for the
cadmium red line, is known, an approximate value of [lambda]/[lambda]'
will usually suffice to determine what integral value must be assigned
to P', and thence by (16) to allow of the calculation of the corrected
ratio [lambda]'/[lambda].

In order to find P we may employ a modified form of (16), viz.,

P' [lambda] / x^2 x'^2 \
--- = --------- ( 1 + --- - ---- ) (17).
P [lambda]' \ 8 8 /

using spectrum lines, such as the cadmium red and the cadmium green,
for which the relative wave-lengths are already known with accuracy
from A. A. Michelson's work. To test a proposed integral value of P
(cadmium red), we calculate P' (cadmium green) from (17), using the
observed values of x, x'. If the result deviates from an integer by
more than a small amount (depending upon the accuracy of the
observations), the proposed value of P is to be rejected. In this way
by a process of exclusion the true value is ultimately arrived at
(Rayleigh, _Phil. Mag._, 1906, 685). It appears that by Fabry and
Perot's method comparisons of wave-lengths may be made accurate to
about one-millionth part; but it is necessary to take account of the
circumstance that the effective thickness t of the plate is not
exactly the same for various wave-lengths as assumed in (16).

S 9. _Newton's Diffusion Rings._--In the fourth part of the second book of his _Opticks_ Newton investigates another series of rings, usually (though not very appropriately) known as the colours of thick plates. The fundamental experiment is as follows. At the centre of curvature of a concave looking-glass, quicksilvered behind, is placed an opaque card, perforated by a small hole through which sunlight is admitted. The main body of the light returns through the aperture; but a series of concentric rings are seen upon the card, the formation of which was proved by Newton to require the co-operation of the two surfaces of the mirror. Thus the diameters of the rings depend upon the thickness of the glass, and none are formed when the glass is replaced by a metallic speculum. The brilliancy of the rings depends upon imperfect polish of the anterior surface of the glass, and may be augmented by a coat of diluted milk, a device used by Michel Ferdinand, duc de Chaulnes. The rings may also be well observed without a screen in the manner recommended by Stokes. For this purpose all that is required is to place a _small_ flame at the centre of curvature of the prepared glass, so as to coincide with its image. The rings are then seen surrounding the flame and occupying a definite position in space.

The explanation of the rings, suggested by Young, and developed by
Herschel, refers them to interference between one portion of light
scattered or diffracted by a particle of dust, and then regularly
refracted and reflected, and another portion first regularly refracted
and reflected and then diffracted at emergence by the same particle.
It has been shown by Stokes (_Camb. Trans._, 1851, 9, p. 147) that no
regular interference is to be expected between portions of light
diffracted by different particles of dust.

In the memoir of Stokes will be found a very complete discussion of
the whole subject, and to this the reader must be referred who desires
a fuller knowledge. Our limits will not allow us to do more than touch
upon one or two points. The condition of fixity of the rings when
observed in air, and of distinctness when a screen is used, is that
the systems due to all parts of the diffusing surface should coincide;
and it is fulfilled only when, as in Newton's experiments, the source
and screen are in the plane passing through the centre of curvature of
the glass.

As the simplest for actual calculation, we will consider a little
further the case where the glass is plane and parallel, of thickness t
and index [mu], and is supplemented by a lens at whose focus the
source of light is placed. This lens acts both as collimator and as
object-glass, so that the combination of lens and plane mirror
replaces the concave mirror of Newton's experiment. The retardation is
calculated in the same way as for thin plates. In fig. 5 the
diffracting particle is situated at B, and we have to find the
relative retardation of the two rays which emerge finally at
inclination [theta], the one diffracted at emergence following the
path ABDBIE, and the other diffracted at entrance and following the
path ABFGH. The retardation of the former from B to I is 2[mu]t + BI,
and of the latter from B to the equivalent place G is 2[mu]BF. Now FB
= t sec [theta]', [theta]' being the angle of refraction; BI = 2t tan
[theta]'sin[theta]; so that the relative retardation F is given by

R = 2[mu]t{1 + [mu]^(-1) tan [theta]' sin [theta] -sec [theta]'}
= 2[mu]t(1 - cos [theta]').

If [theta], [theta]' be small, we may take

R = 2t[theta]^2/[mu] (1).

as sufficiently approximate.

The condition of distinctness is here satisfied, since R is the same
for every ray emergent parallel to a given one. The rays of one
parallel system are collected by the lens to a focus at a definite
point in the neighbourhood of the original source.

The formula (1) was discussed by Herschel, and shown to agree with
Newton's measures. The law of formation of the rings follows
immediately from the expression for the retardation, the radius of the
ring of n^(th) order being proportional to n and to the square root of
the wave-length.

S 10. _Interferometer._--In many cases it is necessary that the two rays ultimately brought to interference should be sufficiently separated over a part of their course to undergo a different treatment; for example, it may be desired to pass them through different gases.

A simple modification of Young's original experiment suffices to solve
this problem. Light proceeding from a slit at A (fig. 6) perpendicular
to the plane of the paper, falls upon a collimating lens B whose
aperture is limited by two parallel and rather narrow slits of equal
width. The parallel rays CE, DF (shown broken in the figure)
transmitted by these slits are brought to a focus at G by the lens EF
where they form an image of the original slit A. This image is
examined with an eye-piece of high magnifying power. The interference
bands at G undergo displacement if the rays CE, DF are subjected to a
relative retardation. Consider what happens at the point G, which is
the geometrical image of A. If all is symmetrical so that the paths
CE, DF are equal, there is brightness. But if, for example, CE be
subjected to a relative retardation of half a wave-length, the
brightness is replaced by darkness, and the bands are shifted through
half a band-interval.

An apparatus of this kind has been found suitable for determining the
refractivity of gases, especially of gases available only in small
quantities (_Proc. Roy. Soc._, 1896, 59, p. 198; 1898, 64, p. 95).
There is great advantage in replacing the ordinary eye-piece by a
simple cylindrical magnifier formed of a glass rod 4 mm. in diameter.
Under these conditions a paraffin lamp sufficed to illuminate the slit
at A, and allowed the refractivities of gases to be compared to about
one-thousandth part.

If the object be to merely see the bands in full development the
lenses of the above apparatus may be dispensed with. A metal or
pasteboard tube 10 in. long carries at one end a single slit
(analogous to A) and at the other a double slit (analogous to C, D).
This double slit, which requires to be very fine, may be made by
scraping two parallel lines with a knife on a piece of silvered glass.
The tube is pointed to a bright light, and the eye, held close behind
the double slit, is focused upon the far slit.

S 11. _Other Refractometers._--In another form of refractometer,
employed by J. C. Jamin, the separations are effected by reflections
at the surfaces of thick plates. Two thick glass mirrors, exactly the
same in all respects, are arranged as in fig. 7. The first of the two
interfering rays is that which is reflected at the first surface of
the first reflector and at the second surface of the second reflector.
The second ray undergoes reflection at the second surface of the first
reflector and at the first surface of the second reflector. Upon the
supposition that the plates are parallel and equally thick, the paths
pursued by these two rays are equal. P represents a thin plate of
glass interposed in the path of one ray, by which the bands are
shifted.

In Jamin's apparatus the two rays which produce interference are
separated by a distance proportional to the thickness of the mirrors,
and since there is a practical limit to this thickness, it is not
possible to separate the two rays very far. In A. A. Michelson's
interferometer there is no such restriction. "The light starts from
source S (fig. 8) and separates at the rear of plate A, part of it
being reflected to the plane mirror C, returning exactly, on its path
through A, to O, where it may be observed by a telescope or received
upon a screen. The other part of the ray goes through the glass plate
A, passes through B, and is reflected by the plane mirror D, returns
on its path to the starting point A, where it is reflected so as
nearly to coincide with the first ray. The plane parallel glass B is
introduced to compensate for the extra thickness of glass which the
first ray has traversed in passing twice through the plate A. Without
it the two paths would not be optically identical, because the first
would contain more glass than the second. Some light is reflected from
the front surface of the plate A, but its effect may be rendered
insignificant by covering the rear surface of A with a coating of
silver of such thickness that about equal portions of the incident
light are reflected and transmitted. The plane parallel plates A and B
are worked originally in one piece, which is afterwards cut in two.
The two pieces are placed parallel to one another, thus ensuring exact
equality in the two optical paths AC and AD" (see Michelson,
_Light-Waves and their Uses_, Chicago, 1903).

The adjustments of this apparatus are very delicate. Of the fully
silvered mirrors C, D, the latter must be accurately parallel to the
image of the former. For many purposes one of the mirrors, C, must be
capable of movement parallel to itself, usually requiring the use of
very truly constructed ways. An escape from this difficulty may be
found in the employment of a layer of mercury, standing on copper, the
surface of which automatically assumes the horizontal position.

Michelson's apparatus, employed to view an extended field of
homogeneous light, exhibits Haidinger's rings, and if all is in good
order the dark parts are sensibly black. As the order of interference
increases, greater and greater demand is made upon the homogeneity of
the light. Thus, if the illumination be from a sodium flame, the rings
are at first distinct, but as the difference of path increases the
duplicity of the bright sodium line begins to produce complications.
After 500 rings, the bright parts of one system coincide with the dark
parts of the other (Fizeau), and if the two systems were equally
bright all trace of rings would disappear. A little later the rings
would again manifest themselves and, after 1000 had gone by, would be
nearly or quite as distinct as at first. And these alternations of
distinctness and indistinctness would persist until the point was
reached at which even a single sodium line was insufficiently
homogeneous. Conversely, the changes of _visibility_ of the rings as
the difference of path increases give evidence as to the duplicity of
the line. In this way Michelson obtained important information as to
the constitution of the approximately homogeneous lines obtained from
electrical discharge through attenuated metallic vapours. Especially
valuable is the vacuum tube containing cadmium. The red line proved
itself to be single and narrow in a high degree, and the green line
was not far behind.

But although in Michelson's hands the apparatus has done excellent
spectroscopic work, it is not without its weak points. A good deal of
labour is required to interpret the visibility curves, and in some
cases the indications are actually ambiguous. For instance, it is
usually impossible to tell on which side of the principal component a
feebler companion lies. It would seem that for spectroscopic purposes
this apparatus must yield to that of Fabry and Perot, in which
multiple reflections are utilized; this is a spectroscope in the
literal sense, inasmuch as the constitution of a spectrum line is seen
by simple inspection. (R.)

FOOTNOTE:

[1] The word "interference" as formed, on the false analogy of such
words as "difference," from "to interfere," which originally was
applied to a horse striking (Lat. _ferire_) one foot or leg against
the other.

INTERIM, originally a Latin word for "in the meantime." The word was hence applied to certain edicts and decrees passed by the emperor and the diets during the reformation in Germany with the object of _temporarily_ settling a controversy. These "interims" regulated points of religious and ecclesiastical difference until they could be decided by a general council. The best example of such a _modus vivendi_ is the Augsburg Interim of 1548, drawn up by Michael Helding, Julius von Pflug and John Agricola (a medievalist, an Erasmian, and a conservative Lutheran) at the bidding of Charles V., and accepted by the diet. It was an ambiguous document, teaching from the Roman Catholic side transubstantiation, the seven sacraments, adoration of the Virgin and saints, and papal headship, and from the Protestant, justification by faith, marriage of priests, the use of the cup by the laity. Maurice of Saxony was permitted to vary the interim for his dominions, and his edition was called the Leipzig Interim. An earlier interim was that of Regensburg, 1541.

INTERLACED ARCHES, the term for a scheme of decoration employed in Romanesque and Gothic architecture, where arches are thrown from alternate piers, interlacing or intersecting one another. In the former case, the first arch mould is carried alternately over and under the second, in the latter the mouldings actually intersect and stop one another. An example of the former exists in St Peter's in the East, Oxford, and of the latter in St Joseph's chapel, Glastonbury, and in the cathedral of Bristol.

INTERLAKEN, a Swiss town (1864 ft.) in the canton of Berne, situated on the flat plain (_Bodeli_) between the lakes of Brienz (E.) and of Thun (W.), and connected by steamer, as well as by railway (17(1/2) m.) with the town of Thun. It is built on the left bank of the Aar, and grew up around the religious house of Austin Canons, founded about 1130 and suppressed in 1528. In the surviving buildings of the convent religious services (Anglican, Scottish Presbyterian and French Protestant) are now held, while the more modern castle is occupied by offices of the Cantonal Government. The fine and well-shaded avenue called the _Hoheweg_ runs through the main portion of the town, and is lined on the north side by a succession of huge hotels and the large Kursaal. Interlaken is much frequented in summer, partly because of the glorious view of the Jungfrau (13,669 ft.) which it commands to the south, and partly because it is the best starting-point for many excursions, as to Schynige Platte, Lauterbrunnen and Grindelwald. The lines serving these places all start from the eastern railway station (that from Thun reaches the western or main railway station), whence steamers depart for the Giessbach Falls, Brienz and Meiringen, on the way to Lucerne or to the Grimsel Pass. In 1900 the population of Interlaken was 2962 (mainly Protestant and German-speaking). Opposite Interlaken, and on the right bank of the Aar is Unterseen (in 1900, 2607 inhabitants), which was built in 1280 by Berthold von Eschenbach.

See _Fontes rerum Bernensium_ (original documents up to 1366) (8
vols., Berne, 1883-1903); _Die Regesten des Klosters zu Interlaken_
(Coire, 1849); E. Tatarinoff, _Die Entwickelung der Probstei
Interlaken im XIII. Jahrhundert_ (Schaffhausen, 1892).
(W. A. B. C.)

INTERLOPER, one who interferes in affairs in which he has no concern. This word, with the verbal form "to interlope," first appears at the end of the 16th and beginning of the 17th century in connexion with the interference of unauthorized persons in the trading monopoly of the Russia Company and later of the East India Company. The _New English Dictionary_ quotes from H. Lane (1590), _Hakluyt's Voyages_, "From those parts the Muscovites were furnished out of Dutchland by enterlopers with all arts and artificers and had few or none by us," and also from the _Minutes of the Court of the East India Company_, 22nd of February 1615, "to examine all suspected personnes that intend interlopinge into the East Indies or Muscovy." Edward Phillips (_New World of Words_, 1658) defines interlopers at common law as those "that without legal authority intercept the trade of a company, as it were Interleapers." The word appears to be of English origin, for the Dutch _enterlooper_, smuggler, often given as the source, was taken from English, as was the French _interlope_. The word is a compound of _inter_, between, and _lope_, a dialectal variant of "leap." A common word for a vagrant, or "straggler," as it is defined, was till 1580 "landloper," and the combination of "straggler" and "interloper" is found in _Horsey's Travels_ (Hakluyt Soc.), 1603-1627, "all interlopers and straglyng Englishmene lyving in that country."

INTERNATIONAL, THE. The International Working Men's Association, commonly called "The International," was formed at London in 1864. It was a society of working men of all nations, somewhat like a cosmopolitan trades union, but bearing a still closer resemblance to an international social science association for discussing and furthering the rights of labour. The occasion of its formation was the visit of some French workmen to the London Exhibition of 1862. In the course of their visit the labour question was discussed, and a desire for the further interchange of ideas expressed. Nothing decisive was done till 1864, when a great public meeting of working men of all nations was held at St Martin's Hall, London, and a provisional committee was appointed to draft the constitution of the new association.

The first four congresses of the International, held at Geneva (September 1866), Lausanne (1867), Brussels (1868), and Basel (1869), marked the rapid development of the association. It gained its first triumph in the effectual support of the bronze-workers at Paris during their lock-out in 1867; and it repeatedly aided the English unionists by preventing the importation of cheap labour from the continent. It soon spread as far east as Poland and Hungary, and it had affiliated societies with journals devoted to its cause in every country of western Europe.

It was supposed to be concerned in all the revolutionary movements and agitations of Europe, gaining notoriety as the rallying point of social overthrow and ruin. Its prestige, however, was always based more on the vast possibilities of the cause it represented than on its actual power. Its organization was loose, its financial resources insignificant; the continental unionists joined it more in the hope of borrowing than of contributing support. At the successive congresses its socialistic tendencies became more and more pronounced; it declared its opposition to private property not only in railways but in mines and the soil, holding that these should revert to the community. Even the principle of inheritance was saved only by a narrow majority. In 1869 M. Bakunin, the Russian socialist or nihilist, with his party joined the association, and at once asserted his character as the "apostle of universal destruction."

The relation of the association to the communal rising at Paris in the spring of 1871 has been the subject of much dispute. It is now agreed that the International as such had no part either in originating or conducting it; some of its French members joined it, but only on their individual responsibility. Its complicity after the event is equally clear. After the fall of the commune the general council of London, Karl Marx included, issued a long and trenchant manifesto, approving its action and extolling the "glorious vanquished." From this point the decline and fall of the association is to be dated. The English unionists, intent on more practical concerns at home, never took a deep interest in its proceedings; the German socialists were hindered by law from corporate action; America was too remote. But it found its worst enemies amongst its own friends; the views of Marx and his school were too moderate for the universally subversive principles of M. Bakunin and the radical Swiss federation of the Jura. It came to a rupture at the congress of 1872, held at the Hague, when Bakunin, being outvoted and "excommunicated" by the Marx party, formed a rival International, which found its chief support in Spain and Italy. Wearied of its European contentions and desirous to form a basis of operation in America, the Marx International now transferred the seat of its general council to New York; but it survived just long enough to hold another congress at Geneva in 1874, and then quietly expired.

The party of destruction styling themselves "autonomists" had a bloodier history. The programme of this party was to overturn all existing institutions, with the view to reconstructing them on some vague communal basis such as had been tried at Paris in 1871. It endeavoured to realize this in the great communal risings in southern Spain in 1873, when its adherents set up their peculiar form of government at Barcelona, Seville, Cadiz and Cartagena--at the last-mentioned place also seizing part of the ironclad fleet of Spain. As at Paris, they failed in leadership and organization, and were suppressed, though not without difficulty, by the national troops. The "autonomists" lingered on till 1879. The collapse was complete of an association which once extended from Hungary to San Francisco, and alarmed the minds of men with visions of universal ruin.

See Villetard, _Histoire de l'Internationale_ (Paris, 1871); Testut,
_L'Internationale_ (Paris, 1871); Onslow Yorke, _Secret History of the
International_ (London, 1871); J. Rae, _Contemporary Socialism_; also
the articles MARX and SOCIALISM.

INTERNATIONAL LAW, the general term for the law governing the relations and intercourse of states with one another. The parties in its application are states (see STATE) and not nations, so that the word "international" does not accurately limit the scope of the subject. Nor do authors always confine themselves to its proper limitation. Thus the rules relating to nationality and naturalization, extradition, patents, trade marks, &c., which affect states on the one side and foreign persons on the other, are generally included among the subject-matter of International Law. There is a special branch of International Law known as Private International Law (see INTERNATIONAL LAW, PRIVATE) which deals exclusively with the relations of persons belonging to different states, in which states as such are not parties.

The term "international" was first used by Bentham. His explanation of the new term was as follows:--

"The word _international_, it must be acknowledged, is a new one;
though, it is hoped, sufficiently analogous and intelligible. It is
calculated to express, in a more significant way, the branch of law
which goes commonly under the name of "law of nations," an appellation
so uncharacteristic that, were it not for the force of custom, it
would seem rather to refer to internal jurisprudence. The chancellor
d'Aguesseau has already made, I find, a similar remark; he says that
what is commonly called _droit des gens_ ought rather to be termed
_droit entre les gens_. There remain then the mutual transactions
between sovereigns as such, for the subject of that branch of
jurisprudence which may be properly and exclusively termed
international."[1]

There has been much controversy as to the aptness of the use of the word "law" in this connexion. "International law," said the 3rd marquess of Salisbury in a speech on the establishment of a Court of International Arbitration, "has no existence in the sense in which the term 'law' is usually understood. It depends generally upon the prejudices of writers of text-books. It can be enforced by no tribunal, and therefore to apply to it the phrase 'law' is to some extent misleading."[2] This has been more or less the view not only of most British statesmen but also of many practical English jurists. It found one of its most emphatic exponents in Lord Chief-Justice Coleridge. "Strictly speaking," he observed in his judgment on the Franconia case,[3] "international law is an inexact expression, and it is apt to mislead, if its inexactness is not kept in mind. Law implies a lawgiver and a tribunal capable of enforcing it and coercing its transgressors, but there is no common lawgiver to sovereign states, and no tribunal has the power to bind them by decrees or coerce them if they transgress. The law of nations is that collection of usages which civilized states have agreed to observe in their dealings with one another. What these usages are, whether a particular one has or has not been agreed to, must be matter of evidence. Treaties and acts of states are but evidence of the agreement of nations, and do not, in England at least, _per se_ bind the tribunals. Neither certainly does a consensus of jurists, but it is evidence of the agreement of nations on international points, and on such points, when they arise, the English courts give effect as part of English law to such agreement."

In opposition to this view may be cited the more recent one expressed by Lord Russell of Killowen, who challenged Lord Coleridge's view as "based on too narrow a definition of law, a definition which relies too much on force as the governing idea." "If," he added, "the development of law is historically considered it will be found to exclude that body of customary law which in early stages of society precedes law. As government becomes more frankly democratic, laws bear less and less the character of commands imposed by a coercive authority, and acquire more and more the character of customary law founded on consent.... I claim that the aggregate of the rules to which nations have agreed to conform in their conduct towards one another are properly to be designated International Law."[4] This recalls Blackstone's definition: "The law of nations is a system of rules, deducible by natural reason, and established by universal consent among the civilized inhabitants of the world, in order to decide all disputes, to regulate all ceremonies and civilities, and to ensure the observance of justice and good faith in that intercourse which must frequently occur between two or more independent states, and the individuals belonging to each."[5] The current English narrower view owes its origin chiefly to the influence of John Austin, and the current broader one to that of Sir Henry Maine.[6] The increasing popularity of references to international arbitration (see ARBITRATION, INTERNATIONAL), the adoption of a large number of special treaties making such references compulsory in certain cases, the establishment of and increasing recourse to the court for the decision of difficulties between states created by The Hague "Convention for the pacific settlement of disputes between States" of 1899 (see PEACE), the adoption of fixed rules of law in the international conventions in 1899, 1907 and 1909 dealing with many of the most controversial questions of international usage, have so transformed the subject that if, as Lord Coleridge said, law implies a lawgiver and a tribunal capable of enforcing it, these conditions are now at any rate partly fulfilled. We shall see below to what extent it may be necessary to regard power of enforcement against transgressors as requisite to give international law the character of law properly so-called.

_Sanctions._--The subject of the enforcement of International Law, or its "sanctions," has given rise to much controversy. The word "sanction" is derived from the Lat. _sanctio_, which in turn is derived from _sancire_, to consecrate. In its original sense _sanctio_ means consecration. From this followed the sense of religious obligation. Thus _sancire legem_ is used by Roman writers as meaning that observance was made obligatory, but without reference to the idea of there being a remedy or penalty for non-observance. With the development of an organized judicial system the religious or moral obligation was displaced by the growth of remedial procedure. Cicero observes of some legal restrictions, _hoc non sancitur lege civili_ (this is not consecrated by the civil law, i.e. with penalties). A collateral sense of the word grew up which meant ratification, as where Cicero speaks of _sancire acta Caesaris_ or of _sancire foedus_.

Bentham, who worked out the theory of legal sanctions as applied to modern law, describes them as equivalent to pleasures and pains derived from four different sources. These are physical, political, moral and religious. The first three belong to experience in the present life, the fourth to that in the present life or hereafter.[7]

Austin's analysis of this vague subdivision led him to a more precise determination of the relationship of sanctions to law, viz. that a law properly so-called is a command and its sanction is the power to enforce obedience to it. Stated briefly, any other kind of law according to Austin is not positive law but merely called so by analogy. Applying this test to International Law he concludes that the law obtaining between nations is not positive law; for every positive law is set by a given sovereign to a person or persons in a state of subjection to its author. The law obtaining between nations is only law set by general opinion, with duties which are only enforced by moral sanction; by fear on the part of nations, or by fear on the part of a sovereign, of provoking general hostility, and incurring its probable evils, in case they should violate maxims generally respected.[8]

Sir H. Maine's somewhat indirect answer to Austin may now be taken as the view held at least by British theoretical writers. "Austin," he said, "has shown, though not without some straining of language, that the sanction is found everywhere, in positive law, civil and criminal. This is, in fact, the great feat which he performed, but some of his disciples seem to me to draw the inference from his language that men always obey rules from fear of punishment. As a matter of fact this is quite untrue, for the largest number of rules which men obey are obeyed unconsciously, from a mere habit of mind. Men do sometimes obey rules for fear of the punishment which will be inflicted if they are violated, but, compared with the mass of men in each community, this class is but small; probably it is substantially confined to what are called the criminal classes, and for one man who refrains from stealing or murdering because he fears the penalty there must be hundreds of thousands who refrain without a thought on the subject."[9]

The view, however, that a law is not devoid of binding character because there is no authority to enforce its observance hardly requires justification at the present day. The fact that any well-established international usage is observed, and that states invariably endeavour to answer any reproach of departing from such usage by explanations showing that the incriminated act is justified by recognized rules of International Law, is evidence of its binding character. As the late Professor Rivier, one of the leading authorities on Roman Law, as well as an international jurist of eminence, has expressed it: "The law of nations is positive law because states wish it to be so. They recognize its compulsory character and proclaim it. As they are their own legislators and make their common laws by express or tacit consent, they attest explicitly and implicitly their conviction that its principles are binding upon them, as judicial principles, as law. Innumerable public acts, affirmations, declarations and conventions are there to prove it. On the other hand, never in any published official act of the present age, verbal or written, has a state dared to declare that it did not consider itself bound by the law of nations and its principles."[10] States, as Professor Rivier says, have again and again solemnly declared their determination to abide by the principles of International Law. Witness the Declaration of Aix-la-Chapelle of November 15, 1818, in which the representatives of five powers, Austria, France, Great Britain, Russia and Prussia, solemnly stated that "the sovereigns in forming this august union have regarded as its fundamental basis their unchangeable resolution never to depart, either amongst themselves or in their relations with other states, from the strictest observance of the principles of the law of nations, principles which, in their application to a permanent state of peace, can alone effectively guarantee the independence of each government and the stability of the general association." In the negotiations for the Treaty of London concerning the Black Sea (March 13, 1871), at which seven powers were represented, Austria-Hungary, France, Germany, Great Britain, Italy, Russia and Turkey, a resolution on the sanctity of treaties was annexed to the first protocol, stating that the plenipotentiaries recognize that it is an essential principle of the law of nations that "no power can liberate itself from the engagements of a treaty, nor modify the stipulations thereof, unless with the consent of the contracting powers by means of an amicable arrangement." Even in 1908, when Austria-Hungary proceeded to the annexation of Bosnia-Herzegovina without obtaining the prior assent of the high contracting powers, who under the treaty of Berlin of 1878 had granted her temporary occupation of the annexed provinces, the protests of the powers concerned were answered by Austria-Hungary declaring that she had done nothing contrary to the law of nations or affecting the sanctity of treaties, because the powers had given their tacit consent to the practical transformation of her temporary into a permanent occupation.

The public opinion of the civilized world, in fact, plays in an ever-increasing degree the part of a sanctioning authority. With the growth of international intercourse and international interdependence the danger of isolation or of discredit or even of "boycotting" becomes a matter of increasing importance in the conduct of states. The national press and periodical literature, with exceptions no doubt, are among the chief factors in the development of this public opinion, but it is by no means dependent upon them. Personal intercourse among citizens of the same country, and between statesmen, politicians and citizens of different countries has a still greater effect in the creation of the mental attitude of nations towards each other. This exposes any departure from recognized usage or any disregard for international obligations to such reprobation throughout the whole world, that, far from taking advantage of the absence of any coercive method of enforcing obedience to the principles of international law, states compete with each other in asserting their strict fidelity to such principles. And now successive diplomatic conferences have codified many of the chief branches of international usage, thus diminishing the possible cases in which states can take advantage of the uncertainty of the law and, by quibbling over its interpretation, escape from its obligations.

_Sources and Foundations._--It is usual, following Wheaton's classification,[11] to enumerate the sources of International Law in the following groups: text-writers of authority as witnesses of usage; treaties of peace, alliance and commerce; ordinances of particular states, prescribing rules for the conduct of their commissioned cruisers and prize tribunals; adjudications of international tribunals; written opinions of official jurists given confidentially to their own government; history of wars, negotiations, treaties and other transactions relating to the public intercourse of nations. It is in these different classes of opinions and precedents that writers have been in the habit of searching for those arguments and analogies on which have been built up the system and principles called International Law.

Wheaton, it is seen, regarded text-writers as witnesses of the usage of nations. He explains his meaning as follows: "Without wishing to exaggerate the importance of these writers, or to substitute in any case their authority for the principles of reason, it may be affirmed that they are generally impartial in their judgment. They are witnesses of the sentiments and usages of civilized nations, and the weight of their testimony increases every time that their authority is invoked by statesmen, and every year that passes without the rules laid down in their works being impugned by the avowal of contrary principles." This distinguished writer's quasi-explanation of the sources of International Law is extremely vague. He masses together cause and effect, private and public opinions, usage and exceptions. Professor Oppenheim has endeavoured to give a more scientific explanation of the growth and development of International Law, and objects to calling sources of International Law what are mere factors influencing its growth:--

"... Custom and treaties," he observes, "are the two exclusive sources
of the Law of Nations. When writers on International Law frequently
enumerate other sources besides custom and treaties they confound the
term 'source' with that of 'cause'[12] by calling sources of
International Law such factors as influence the gradual growth of new
rules of International Law without, however, being the historical
facts out of which these rules receive their legal force. Important
factors of this kind are: Opinions of famous writers on International
Law, decisions of prize courts, arbitral awards, instructions issued
by the different states for the guidance of their diplomatic and other
organs, state papers concerning foreign politics, certain municipal
laws, decisions of municipal courts. All these and other factors may
influence the growth of International Law either by creating usages
which gradually turn into custom, or by inducing the members of the
Family of Nations to conclude such treaties as stipulate legal rules
for future international conduct.

"A factor of the special kind which also influences the growth of
International Law is the so-called comity (_Comitas gentium,
Convenance et courtoisie internationale, Staatengunst_). In their
intercourse with one another states do observe not only legally
binding rules and such rules as have the character of usages, but also
rules of politeness, convenience and goodwill. Such rules of
international conduct are no rules of law, but of comity. The Comity
of Nations is certainly not a source of International Law, as it is
distinctly the contrast to the Law of Nations. But there can be no
doubt that many a rule which formerly was a rule of International
Comity only is nowadays a rule of International Law. And it is
certainly to be expected that this development will go on in future
also, and that thereby many a rule of present International Comity
will in future become one of International Law."[13]

Precedents.

Italian influence.

We prefer to regard International Law as deriving the rules composing it from practically the same sources as domestic law, and to attribute to text-writers more or less the same value in its development as in that of the private law of nations. The same primary rules of conduct are appealed to between states as between individuals, and precedents play exactly the same part wherever human actions are concerned. In both cases what has been done before commends itself when the responsibility of taking steps pledging the future is concerned. Statesmen on whom great responsibility impends, on whom the conduct of momentous negotiations has devolved, and who will have to render an account of their work to the sovereign or nation they represent, preserve an argument in their own favour in departing as little as possible from any course taken in previous similar circumstances. Precedents, moreover, are arguments for acceptance by their adversaries or counter-negotiators. In fact, in diplomacy even more than in matters of domestic government precedents play a dominant part in the growth of usage. These precedents are often in themselves originally local usages, such as grew up in the intercourse of the Italian communities. Italy, in fact, served as a laboratory for early diplomatists and writers. It was in the intercourse of these active and ambitious states that grew up the very notion of a foreign diplomacy and the necessity of rules of conduct in this miniature Europe, with its perpetual antagonisms and jealousies, its balance of power, its idea of a state distinct from a nation and of a community of states elbowing each other in their daily contact. It was there that grew up the institution of passports, the distinction between armed forces and civilians, international comity, and in fact the very notion that states have an interest in the observance of law and order among them. In the same way the active commercial intercourse in the Mediterranean led, in the common interest, to the development of rules of the sea in time of peace, and later to others in time of war.

Thirty Years' War.