274 TEE POPULAR SCIENCE MONTHLY. 



built up. Perhaps I may be excused for noting a sample of these early- 

 speculations, already possibly known to a few of my readers, but which 

 here finds a more suitable place than that which it formerly occupied. 



Sitting, in the summer of 1855, with my friend Dr. Debus under 

 the shadow of a massive elm on the bank of a river in Normandy, the 

 current of our thoughts and conversation was substantially this : We 

 regarded the tree above us. In opposition to gravity its molecules had 

 ascended, diverged into branches, and budded into innumerable leaves. 

 What caused them to do so — a power external to themselves, or an 

 inherent force ? Science rejects the outside builder ; let us, therefore, 

 consider from the other point of view the experience of the present 

 year. A low temperature had kejDt back for weeks the life of the vege- 

 table world. But at length the sun gained power — or, rather, the 

 cloud-screen which our atmosphere had drawn between him and us was 

 removed — and life immediately kindled under his warmth. But what 

 is life, and how can solar light and heat thus affect it ? Near our elm 

 was a silver-birch, with its leaves rapidly quivering in the morning air. 

 We had here motion, but not the motion of life. Each leaf moved as 

 a mass under the influence of an outside force, while the motion of life 

 was inherent and molecular. How are we to figure this molecular mo- 

 tion — the forces which it implies, and the results which flow from them ? 

 Suppose the leaves to be shaken from the birch-tree and enabled to 

 attract and repel each other. To fix the ideas, suppose the point of 

 each leaf to repel all other points and to attract the other ends, and the 

 root of each leaf to repel all other roots, but to attract the points. The 

 leaves would then resemble an assemblage of little magnets abandoned 

 freely to the interaction of their own forces. In obedience to these 

 they would arrange themselves, and finally assume positions of rest, 

 forming a coherent mass. Let us suppose the breeze, which now causes 

 them to quiver, to disturb the assumed equilibrium. As often as dis- 

 turbed there would be a constant efi"ort on the part of the leaves to re- 

 establish it ; and in making this effort the mass of leaves would pass 

 through different shapes and forms. If other leaves, moreover, were 

 at hand endowed with similar forces, the action would extend to them 

 — a growth of the mass of leaves being the consequence. 



We have strong reason for assuming that the ultimate particles of 

 matter — the atoms and molecules of which it is made up — are endowed 

 with forces coarsely typified by those here ascribed to the leaves. The 

 phenomena of crystallization lead, of necessity, to this conception of 

 molecular polarity. Under the operation of such forces the molecules 

 of a seed, like our fallen leaves in the first instance, take up positions 

 from which they would never move if undisturbed by an external im- 

 pulse. But solar light and heat, which come to us as waves through 

 space, are the great agents of molecular disturbance. On the inert 

 molecules of seed and soil these waves impinge, disturbing the atomic 



