The “infinitely small” presents occasionally surprising likeness to the “infinitely large.”
In this manner we can form a conception of the growth of the wonderful structure which has brought forth the majority of the stellar bodies that we discern. The spiral nebulæ visible at the Galactic poles are similar formations but probably of far more modest dimensions. They may compare to the Milky Way as the smaller planets to the Sun. According to recent investigations the spiral nebulæ seem also to possess an enormous velocity and they have probably invaded the Milky Way from without.
As previously stated, an exceedingly remarkable conception of the Milky Way exists among the Mexicans. To them it is the Matrix of all and gave birth to the stars, the most important of which are the Sun, the Moon, and Venus. This idea evidently agrees very well with the results of investigations in the last few years.
Finally, a few words about the extent of the Milky Way. So far we have not been able to measure it; only rather uncertain approximations are possible. Wolf estimates the diameter, that is the distance between the two spirals at the point where the Sun now is, to be about 10,000 times the distance from the Sun to the nearest fixed star, Alpha in Centaurus, which distance on the other hand is about 10,000 times the distance from the Sun to the remotest known planet, Neptune, or 300,000 times that from Sun to Earth. Expressed in the usual units, we arrive at 40,000 light years or 400,000 trillion kilometres (240,000 trillion miles). Lord Kelvin makes another estimate of 6000 light years, that is seven times smaller. The mean diameter of the nebula proper might be about five times larger, in round figures one hundred thousand light years, or one billion billion kilometres (600 million billion miles).
Like a monstrous octopus, the Milky Way swims in the fathomless ether-sea. Its dimensions are about as many times larger than those of the earth as that globe is larger than an atom. This has caused the gifted Irish physicist Fournier D’Albe to consider the celestial globes as atoms, out of which systems of the order of the Milky Way are constructed in the same manner as the earth and other stellar bodies are upbuilt with atoms, invisible to us and yet measured with an incredible degree of accuracy.
Fournier D’Albe goes further still. In poetic flight he does not hesitate to endow the Milky Way organism with life. Its evolution cannot be denied a certain similarity to the processes of life. The great nebula owes its origin to the union of two individuals, two nebulosities, who met in their course through boundless space. There floated the newborn extending its tentacles in the cool ether-waves and gained substance and strength through the smaller beings which the surging billows brought within its reach. It has now attained the zenith of its evolution, and is breaking up into molecules, or solar systems, which again are composed of stellar bodies, or atoms within the molecule. In violent exuberance of youth these rush through space in fulfilment of their individual life. Many will in due time undoubtedly become dust again and then serve to nourish a new youthful nebula. Others succumb to a freezing-death but will be restored to life in collision with a nebulosity or some other stellar body and give form to “new stars” or planetary clouds. Again and again shall the starry mists go through the cycle of existence and after a lifetime, whose duration stands in proportion to their dimensions, i. e. may be estimated to billions of billions of years, give rise to new celestial beings. Thus shall it for ever continue in an eternal rhythm.
CHAPTER III
THE CLIMATIC IMPORTANCE OF WATER VAPOUR
When Aristotle, for two thousand years our leading savant in cosmography, about twenty-three centuries ago stated the foundation of his natural science, he laid down as the important principles: moisture and heat and their opposites; because the four elements out of which everything was made, were: earth, characterized by dryness and cold; water, which was moist and cold; air, which combined moisture with heat; and lastly fire, which stood for dryness and heat. Undoubtedly he was considering the requisites of life, which may be designated as humidity and heat. We have seemingly agreed that all life originates in the sea, so that moisture can be considered the first requirement for its appearance on the earth. As to heat, life is destroyed by frost and favoured by increased warmth, at least to a certain point, about 35° to 40° C. (95° to 104° Fahrenheit), which temperature is most propitious to the development of life, while a further increase is detrimental, so that already below the boiling point of water life suffers more harm than at temperatures below freezing. In fact, the geologists have found that the different epochs in earth’s evolution are best characterized by their humidity or dryness. To arrive at a clear conception in these matters we shall briefly survey our present knowledge of the importance for the evolution of life on earth that we should attach to the humid and to the dry periods or localities.
We are all familiar with the heavy, moisture-laden warmth which meets us when we enter a hothouse. It is particularly favourable to the growth of plants and to the prosperity of the lower animals. To the higher animals and to man, the humid heat is not so beneficial. In the open such hothouse air exists only in the tropics. Particularly the Congo region and the parts of Brazil adjoining the Amazon River are remarkable for their humid heat and for their fabulously luxuriant vegetation. From our greatest living climatologist, Julius Hann, I have borrowed the following description of such a clime: