210 THE MECHANISM OF LIFE 



nor in most of the planets that surround the latter (unless we 

 extend the definition of life in a way that we do not contemplate 

 just yet). Even upon our own earth living substance forms only 

 a surface film of incredible tenuity when compared with the 

 dimensions of the planet. It is probably most dense in shallow 

 seas near the land, but even there the mass of organised matter 

 is only a few parts per million of water. In oceanic regions, both 

 at the surface and in the depths, the density of life is much less, i 

 and on the land (when we take account of polar, mountainous, and 

 desert areas) the density is still less. All that is, of course, only 

 the surface of our planet ; in its depths life is very nearly absent. 



From the idealistic standpoint life (in strictness, our own life, 

 or mind) is all that is, for the universe and all the things that 

 science places there are only mental constructions. 



Man, says Pascal, is only a reed, but he is a thinking reed. 

 He is among the least and most fragile of things. But he is also, 

 among the greatest of things ; he is, indeed, greater than all other 

 things, for he can comprehend the universe. 



Life is like Pascal's reed. Anywhere in the universe it is 

 highly improbable that energy exists in such a form as to givej 

 rise to physical changes. Even in this fraction of the universe,] 

 where there is physical change it is also highly improbable that 

 among these activities there are some that exhibit what we call 

 the phenomena of life. In other words, the chance that life exists 

 anywhere in our universe is an infinitesimal of the second order, 



The Physical Nature of Life. If we would try to explain life 

 we must, first of all, be very clear about what we mean by anj 

 " explanation." Consider the motions of the bodies that make 

 up our solar system: the planets revolve round a central sun in 

 elliptical orbits, and the satellites revolve round the planets ; thd 

 sun, planets, and satellites rotate on their own axes, and that 

 latter process, or rotate, while still retaining their inclination to 

 the plane of the ecliptic; the ellipticity of each orbit clumps 

 periodically; the various bodies " nutate " ; each of them perturb^ 

 all the others, and so on through a host of motions. To describe 

 all the latter would be very difficult, and the description would 

 be very hard to understand for anyone who is not an astronomer. 

 But assume that each body has a certain mass, that it had aj 

 certain initial velocity, and that it attracts every other body with 

 a force that depends on the various masses and on the squared 

 of the distances between the bodies. Then all the motions can 



