Brownian Motion

According to M. Gouy, the singular Brownian movement does not obey Carnot’s principle.

The particles which it sets moving would be smaller than the meshes of that tightly drawn net.

They would thus be ready to separate them, and thereby to set back the course of the universe. One can almost see Maxwell’s demon at work. 1

To resume, phenomena long known are gradually being better classified, but new phenomena come to claim their place, and most of them, like the Zeeman effect, find it at once.

Then we have the cathode rays, the X-rays, uranium and radium rays; in fact, a whole world Clerk-Maxwell imagined some supernatural agency at work, sorting molecules in a gas of uniform temperature into:

• (a) those possessing kinetic energy above the average
• (b) those possessing kinetic energy below the average.—[Tr.] of which none had suspected the existence. How many unexpected guests to find a place for!

No one can yet predict the place they will occupy. But I do not believe they will destroy the general unity: I think that they will rather complete it.

On the one hand, the new radiations seem to be connected with the phenomena of luminosity. They not only excite fluorescence, but they sometimes come into existence under the same conditions as that property. They are related to the cause which produces the electric spark under the action of ultra-violet light.

Most important of all, it is believed that in all these phenomena there exist animated ions with velocities far greater than those of electrolytes.

Phosphorescence and the action of light on the spark were regions rather isolated, and consequently somewhat neglected by investigators. It is to be hoped that a new path will now be made which will facilitate their communications with the rest of science.

Not only do we discover new phenomena, but those we think we know are revealed in unlooked-for aspects.

In the free ether the laws preserve their majestic simplicity, but matter properly so called seems more and more complex; all we can say of it is but approximate, and our formulæ are constantly requiring new terms.

But the ranks are unbroken, the relations that we have discovered between objects we thought simple still hold good between the same objects when their complexity is recognised, and that alone is the important thing.

Our equations become, it is true, more and more complicated, so as to embrace more closely the complexity of nature; but nothing is changed in the relations which enable these equations to be derived from each other.

In a word, the form of these equations persists. Take for instance the laws of reflection. Fresnel established them by a simple and attractive theory which experiment seemed to confirm. Subsequently, more accurate researches have shown that this verification was but approximate; traces of elliptic polarisation were detected everywhere.

But it is owing to the first approximation that the cause of these anomalies was found in the existence of a transition layer, and all the essentials of Fresnel’s theory have remained.

We cannot help reflecting that all these relations would never have been noted if there had been doubt in the first place as to the complexity of the objects they connect.

Long ago it was said: If Tycho had had instruments ten times as precise, we would never have had a Kepler, or a Newton, or Astronomy.

It is a misfortune for a science to be born too late, when the means of observation have become too perfect. That is what is happening at this moment with respect to physical chemistry.

The founders are hampered in their general grasp by third and fourth decimal places; happily they are men of robust faith.

As we get to know the properties of matter better we see that continuity reigns.

From the work of Andrews and Van der Waals, we see how the transition from the liquid to the gaseous state is made, and that it is not abrupt.

Similarly, there is no gap between the liquid and solid states, and in the proceedings of a recent Congress we see memoirs on the rigidity of liquids side by side with papers on the flow of solids. With this tendency there is no doubt a loss of simplicity.

Such and such an effect was represented by straight lines; it is now necessary to connect these lines by more or less complicated curves. On the other hand, unity is gained. Separate categories quieted but did not satisfy the mind.

Finally, a new domain, that of chemistry, has been invaded by the method of physics, and we see the birth of physical chemistry. It is still quite young, but already it has enabled us to connect such phenomena as electrolysis, osmosis, and the movements of ions.

From this cursory exposition what can we conclude?

Taking all things into account, we have approached the realisation of unity. This has not been done as quickly as was hoped fifty years ago, and the path predicted has not always been followed; but, on the whole, much ground has been gained.