The smallness of molecules surpasses anything one can imagine. In the gold-beating industry gold-leaf has been obtained so thin that a quarter of a million leaves go to the inch. Each gold-leaf, therefore, has only a thickness of a 1/10,000 of a millimetre. Now, it is composed of molecules a considerable number of which is required to fill up that thickness. Two hundred of them arranged in a line and separated by intervals equal to their own diameters would just fill up the thickness of a gold-leaf.
In experiments made on the action of oil upon the surface of water for calming the waves, it has been found possible to cover 400 square yards on the Lake of Geneva with 20 c.cm. of oil, which reduces the layer of oil also to 1/200,000 of a millimetre. Supposing that under these conditions the molecules of oil are in contact and in a single layer, they would at the most have that diameter.
By mechanical means a millimetre has been divided on a plate of glass into a thousand equal parts. There are animalculæ so small that their whole body placed between two of these divisions does not touch them. These living beings then measure at the most 1/1,000 of a millimetre, or what is nowadays called a micron. They have members, organs, muscles, nerves, etc. These organs are composed of cells and the cells of molecules. If the latter were only a hundredth part of the dimensions of the body (they are probably much smaller), these molecules would measure, if separated by intervals equal to their own size, 1/200,000 of a millimetre as before.
Molecules or atoms, whatever may be the name applied to the ultimate particles of matter, are declared by present-day science to be equal to stellar systems or microcosms.
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This modern teaching of microscopy was anticipated for a long time by thinkers.
In his Commercium Philosophicum, published in 1745, Bernoulli wrote to Leibnitz concerning the imaginary inhabitants of a grain of pepper.
“If these animalculæ had an intelligent mind and were capable of reasoning, they could flatter themselves that they and the drop of liquid which they inhabit constituted the entire universe. Imagine that a small grain of pepper in which under the power of the microscope we discover a million animalculæ had all its parts proportional to the corresponding parts of our world, that is to say, its sun, its fixed stars, its planets with their satellites, its earth, and its mountains, its fields, its forests, its rocks, its rivers, its lakes, its seas, and its diverse animals, can one suppose that the inhabitants of the grain of pepper, these pipericols, who would perceive all objects under the same visual angle and consequently in the same size as we do, would not believe that outside their grain nothing exists, and would have the same right to believe it as we believe that our world includes everything? For, I ask you, what reason or what experience would they have which would convince them of the contrary or would show to these poor little animals that there is another world incomparably greater than their own with inhabitants incomparably greater than themselves?”
Therefore, concludes Bernoulli, if these pipericols cannot know that, who is there among us who knows that this whole visible world is not perhaps a grain in comparison with another world incomparably greater?
The learned geometrician of Basle summarises his idea as follows: “I believe that there can exist in nature other animals who are in size as far above us and ordinary animals as we and our animals are above microscopic animalculæ, and who observe us in our world with their microscopes as we observe that infinite multitude of animalculæ with ours. I go further and maintain that there might be beings incomparably larger again, and I suppose as many degrees upward as are found in going downwards, for I do not see why we should constitute the highest degree.”