On the Formation of Soap-bubbles by the Contact of Alkaline Oleates with Water. By Professor G. QUINCKE, F.R.S.

[Ordered by the General Committee to be printed in extenso.]

SOME years ago I showed that soap-solution could be spread out on the common surface of oil and water or of oleic acid and water. The surface tension is diminished by this spreading more than 80 per cent. The spreading forms vortices in both liquids, and attracts all matter to the centre of spreading. If the soap-solution is formed by the oleic acid in contact with water containing potassium, sodium, or ammonia on the surface of a drop of oil, suspended in water of the same density, near the wall of the glass vessel or near viscous substances, the drop of oil is attracted by the wall or the viscous matter. The formation and the spreading out of soap-solution may be periodical and the movement periodical. If the period is very short the movement is apparently continuous. Oilbubbles filled with water or small bodies covered with very thin films of oil are displaced in the same manner as oil spheres by the spreading of soap-solution.

I think that this new principle of movement will also explain a great many phenomena in organic nature, and I have tried also to explain by this new principle the spontaneous formation of emulsion or foam by the contact of oil (with oleic acid) and alkaline water, the foam-structure and the motion of the protoplasm in the cells of the plants.

Very thin films of oil are sufficient to show this motion by periodical spreading of the solution of very small quantities of soap, so thin and so small that they cannot be seen with the microscope or recognised in any other way.

Recently I have studied the phenomena by the contact of the oleates of potassium, sodium, and ammonia with water. The neutral oleates are dissolved by water, and form a viscous liquid. With more water an acid salt is formed and the alkali is dissolved in the water. These acid salts or acid soaps are not soluble in water, or only slightly soluble in water. By longer contact with water they are dissociated, and form again liquid oleic acid and neutral oleates or soap-solutions.

When small quantities of neutral oleates are placed in contact with water between the cover-glass and the slide, and are examined by a microscope with polarised light, they are found to be covered with thin films of oleic acid. This film dissolves oleate and water, and the diffusion of both substances will bring water to the soap inside the oil-film of oleic acid, and oleate to the water outside the oil-film. The volume of the soap inside the oil-film is increased, the soap-solution formed on the common surface of oil and water is spread out, and now the vortices, excited by the spreading, attract the matter, the soap, and the liquid. In this way are produced very curious forms called myeline by Virchow, who first observed them in putrefied brain. These myeline forms-crystals of soap (with water of crystallisation, covered with the thin oil-films and showing a smooth surface)-are doubly refractive.

The liquid crystals' observed by Professor Lehmann, of Karlsruhe, in fused benzoylcholesterine and fused azoxyanisol are also doubly refracting crystals, covered with a thin film of oily matter formed in the liquid by the fusion.

When more water diffuses through the oil-film to the soap inside there is formed a viscous liquid, a solution of the oleate in a jacket of oleic acid. The movement of the water and the periodical spreading of soap-solution will form long filaments or cylinders of viscous matter covered with an oil-film. The oil-film contracts and forms bubbles in the middle and the ends of the oil-filament. By the spreading of soap solution the bubbles wander along the oil cylinders with different velocities and in different directions. After some time the oil cylinders are deformed and become strings of beads of oleic acid and thin oil-films. The thin oil-films form foam or bubbles filled with water or weak solution of soap.

In the oil-film are distributed lenses or spheres of oil filled with strong or weak soap-solution. Some methylene-blue dissolved in the water is collected or stored up in the oleic acid, so that the coloured oil and the water may be very easily distinguished.

The spheres of oleic acid coloured with methylene-blue are arranged on the edges of the films of the bubbles or spherical films of the foam, and the appearance is similar to the appearance presented by the stars of the Milky Way. The formation of chains of stars, as observed by Professor Max Wolf, and the spiral nebula in Perseus in the excellent photographs of Dr. Roberts, are similar in appearance to the phenomena observed by me in these microscopical oil-films and bubbles.

Fifty years ago Plateau pointed to the analogy of the rotation of the sun and the planets with the rotation of oil-spheres suspended in a mixture of alcohol and water of the same dencity. Now we have a new analogy between the arrangement of matter of the universe by forces acting at very great or very small distances. From the standpoint of our modern physics, with the Newtonian law of gravitation and the law of action of molecular forces, these analogies may appear to be somewhat arbitrary. But we must be able to pass from definite distances to infinitely great or to infinitely small distances of the acting masses, and we can conceive that it may be possible that the difference between the law of gravitation and the law of the molecular forces may disappear, and that we may have the same law for small and great distances; so that the distribution of matter may be accounted for by the same forces, when the masses and the distances of the masses are increased in the same proportion, a million or a billion times.

The work of future generations will decide whether researches on the microscopical oil-foam or on the stars of the universe will give the solution of this problem.

On the Displacements of the Rotational Axis of the Earth. By Professor W. FÖRSTER, Director of the Royal Observatory of Berlin.

[Ordered by the General Committee to be printed in extenso.]

DISPLACEMENTS of the rotational axis of the earth with reference to fixed directions in space have been observed since the earliest ages of astronomical measurement; for such displacements, visible in wanderings of the pole of the apparent diurnal rotation of the celestial sphere among the constellations of fixed stars, exist in such enormous amplitudes, that in their main features they could be detected by the aid of very simple apparatus and observations.

The true law and explanation of these wanderings of the pole remained, nevertheless, a deep mystery till Copernicus lifted the veil by showing that they were only the celestial image of real displacements of the rotational axis of the earth in space, and until Newton came and, combining his discovery of universal gravitation with his deduction of the ellipsoidal figure of the earth, proved that these displacements are due to the actions of the moon and the sun on the earth.

The mathematicians of the eighteenth century completed this explanation by profound researches embracing the full theory of free rotation of a solid system of masses, under the action of various disturbing influences, not only those acting from outwards on the rotating body (as in the case of the sun's and the moon's attractions on the earth), but also those depending upon the condition or changes within the rotating system itself.

Among several interesting results, these investigations pointed out an essential difference between the development of the disturbed rotation in the first and in the second case.

Upon the supposition, corresponding to the real terrestrial conditions of the problem, namely, that all the disturbing influences are relatively small in comparison with the amount of energy represented by the primary rotation of the earth itself, the following distinctions were demonstrated.

Exterior disturbing influences will mainly produce displacements of the axis in space, and corresponding wanderings of the pole among the stars; whilst the simultaneous displacements of the axis in the earth itself, in consequence of the particular conditions of their evolution, remain insensible.

On the contrary, interior conditions and disturbing influences, as those contained in the configurations of the masses, or in changes of the distribution of the masses composing the rotating system, will mainly produce displacements of the rotational axis in the rotating body itself, whilst in this case the simultaneous displacements of this axis in space and the corresponding variations of the position of the pole among the stars remain insensible.

Very soon after these deductions had been made from theory, astronomers began to inquire if also effects of the latter type that is to say, displacements of the rotational axis in the earth-really existed.

According to theory, such displacements ought even to exist when the distribution of the masses composing the earth is not in the slightest degree variable.

It is sufficient for producing such displacements that the position of the rotational axis of the earth is actually not in perfect coincidence with one of its principal axes of inertia, known as the principal axis.

The slightest deviation of the rotational axis from the principal axis has the consequence that the pole of the rotational axis begins and continues to describe a small circle around the pole of the principal axis.

The velocity of this movement depends upon the law of the figure and of the distribution of the masses composing the earth, and the best numerical data for this dependence had given the result that the displacement in question would probably have a period of nearly ten months.

Now all such displacements, possibly measurable with reference to fixed directions in the earth, and insensible with reference to fixed directions in space, could be found in the most favourable way by measuring as exactly and continuously as possible the distance of the pole from the

zenith of the observer's station; in other words, by repeated determinations of geographical latitudes. But, notwithstanding very long and refined determinations of the geographical latitudes at some of the principal observatories, beginning shortly before the middle of the present century, only very uncertain and discordant traces of the phenomena in question were found.

The reason for this want of success is now very clear. Astronomers had limited their researches too narrowly to the last-mentioned typenamely, to the supposed regular ten-monthly periodical movement of the pole of the rotational axis around the pole of the principal axis. Too easily it had been admitted that all the existing variations of the distribution of terrestrial masses were far too small for altering sensibly the position of this principal axis itself.

It was Lord Kelvin, at the Glasgow meeting of the British Association (1876), who first drew the attention of the scientific world to the consideration of the great natural transports of masses of air and water, and of various masses by the water, going on continuously and periodically in the form of currents and circulations of different kinds, as well in the atmosphere as in oceans and rivers, and the effects of the enormous periodical deposits of snow and ice. He showed that these very considerable variations of the distribution of masses on the earth could not only produce sensible displacements of the principal axis of inertia, but that such displacements of this axis could have an amplifying effect on the total amount of displacements of the rotational axis.

For if the principal axis were itself not in a constant position, the theoretically required movement of the rotational axis around the principal axis would become a very complicated movement, differing entirely from the simple form which to that time had appeared in the researches of

astronomers.

This epicyclic character of the movement of the pole of the rotational axis could considerably modify not only the length of the period, but also the whole geometrical character and amplitude of the curve, in such a way that in longer periods epochs of very small variations of latitude could alternate with epochs of considerably increased variations of latitude. Possibly, as a further consequence of this complication of the displacements of the two axes, and as a consequence of the still existing plastic state of certain parts of the earth, as well as by the damping effects of the fluid parts, even progressive-though very slow and unsteady progressivedisplacements of the rotational axis in the earth could still result.

The field of this research was thus decisively cleared by Lord Kelvin; and finally, about four years ago, by the co-operation of some Observatories with the International Geodetic Union, clear evidence was obtained, and in the last three years, with the aid of an expedition sent by the International Union to Honolulu, decisive proofs of such displacements have been found. I consider it a special honour and pleasure to be enabled to submit some of the newest results of this international co-operation to a meeting of the same Association which, twenty years ago, had been witness of the almost prophetic assertions of one of its most illustrious members regarding the real conditions of this important phenomenon.

I have prepared a diagram showing these newest results. In this diagram is given a representation of the wanderings of the pole of the rotational axis of the earth on its surface during the last twenty months, from October 20, 1892, to May 1, 1894.