Dreams of an astronomer

by Camille Flammarion

The conditions necessary to life are the more numerous the more complicated the structure of organic matter. The maximum of requirements is therefore attained in the higher animals and in man.

The simpler the organism, the simpler are its conditions of existence and the greater are in general the possibilities of supporting unfavourable conditions.

Animals and plants living in caves or at great depths under water are deprived of light; they have accommodated themselves to that privation and do not suffer by it. Animals require oxygen in air and in water; plants also require a small quantity of carbonic acid for building up their tissues. There are even animalcule in existence for whom oxygen is a poison. As a general rule, temperatures above 50 degrees centigrade are insupportable.

This is due to the fact that at that temperature albumen, one of the most important substances in the animal organism, coagulates. Inferior beings can resist higher temperatures and even for a short time 100 degrees centigrade, which is the boiling-point of water, but they could not live long. In its liquid form water is indispensable to organic life; life of any duration below zero is impossible because the water contained in every organism would solidify and the parts composing the organism would lose their mobility. Lack of water does, however, not inevitably imply death, and plants particularly can preserve for a long time a latent vitality while deprived of water. Cereals furnish a striking example, for when dried they can preserve their germinating power for years. Although living matter can preserve its vitality so long, it is none the less true that during that period all manifestations of life cease. If therefore the lack of water is perpetual, life must be considered as really suppressed.

Even for the lowest forms of life three conditions must be regarded as essential: water, an atmosphere containing oxygen and carbonic acid, and a temperature between the limits indicated above.

It is therefore really from these three points of view that we must study the heavenly bodies in order to be in a position to judge whether organic life as we know it is possible on them or not. As regards knowing whether that life presents itself under forms comparable to those which we see here, whether there are, for instance, beings analogous to humanity, that is quite another question.

The means at the disposal of astronomy for determining the constitution of the heavenly bodies are of various kinds. We can take into account phenomena which at first sight do not seem adapted to that end.

Direct observation with the help of the telescope enables us to discover the surface details of the planets and any changes which take place in them. Such changes in most cases imply the existence of an atmosphere. Observations of occultations of stars by the Moon or the planets lead to the same result. Theoretical astronomy tells us the distance between the planets and the Sun; physics tell us the quantity of light received by each planet from the Sun; and the period of revolution and the inclination of the planet’s axis tell us about the course of its seasons. Photometry gives us the amount of sunlight reflected by the surface of the planet, and thus furnishes indications concerning certain properties of the planetary surface, properties which permit us to decide with certainty, for instance, whether light is reflected by a solid surface such as the ground or whether the rays do not penetrate so far and are sent back in the upper parts of the atmosphere by lays of clouds.

It is spectrum analysis which furnishes, as we know, the most important auxiliary information; it presents the heavenly bodies to the eye of the mind as the microscope unveils to the eye of the body the marvels of the infinitely small. The rays of light are messengers who, having passed through the spectroscope, bring to us news of the most distant worlds and tell us of the temperature of the fixed stars, of the metals volatilised in their atmospheres, of the incredibly low temperature of the nebulæ and of the gases which envelop the planets.

We do not here wish to intone a hymn to spectrum analysis; we only wish to report briefly and simply what we know of the physical nature of the celestial bodies. But we must admit that the greatest amount of that knowledge is due to the spectroscope.