Science and method / by Henri Poincaré ; translated by Francis Maitland ; with a preface by Bertrand Russell.

Date:
[1914?]
Catalogue details

Licence: In copyright

Credit: Science and method / by Henri Poincaré ; translated by Francis Maitland ; with a preface by Bertrand Russell. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    So that if the first collision multiplied the deviation by a very large number, A, after n collisions it will be multiplied by A”. It will, therefore, have become very great, not only because A is large—that is to say, because small causes produce great effects—but be- cause the exponent n is large, that is to say, because the collisions are very numerous and the causes very complex. Let us pass to a second example. Why is it that in a shower the drops of rain appear to us to be distributed by chance? It is again because of the complexity of the causes which determine their formation. Ions have been distributed through the atmosphere; for a long time they have been sub- jected to constantly changing air currents, they have been involved in whirlwinds of very small dimensions, so that their final distribution has no longer any relation to their original distribution. Suddenly the temperature falls, the vapour condenses, and each of these ions becomes the centre of a raindrop. In order to know how these drops will be distributed and how many will fall on each stone of the pave- ment, it is not enough to know the original position of the ions, but we must calculate the effect of a thousand minute and capricious air currents. It is the same thing again if we take grains of dust in suspension in water. The vessel is permeated by currents whose law we know nothing of except that it is very complicated. After a certain length of time the grains will be distributed by chance, that is to say uniformly, throughout the vessel, and this is entirely due to the complication of the currents If they obeyed some simple law—if, for instance