Cent. (212° Fahr.)—that is to say, that of boiling water,—but even they cannot live long in this temperature. In its liquid form water is indispensable to organic life. Life for any length of time is impossible below 0° Cent. (32° Fahr.), because the water contained in the whole organism would solidify, and the particles comprising the organism would lose their mobility. The want of water, however, does not necessarily involve death, and plants notably can maintain a latent life for a very long time, though deprived of water. The cereals without moisture retain for years the power of germinating.
Grains of maize found with the Egyptian mummies, consequently thousands of years old, have put forth shoots when planted in the earth.
Although organized matter can retain vitality so long, it is no less true that during this period all vital manifestation ceases, so that life can be considered null if the want of water be perpetual. Even with regard to the rudimentary form of life, three conditions must be considered essential: (1) an atmosphere containing oxygen and carbonic acid, (2) water, and (3) a temperature between the limits above indicated.
It is thus from these three points of view that we ought to study the celestial bodies, so as to be able to judge if a simple organic life, such as we understand it, be possible there or not.
The telescope permits us to discover such details of the surface and modifications of the planets as to lead us to conclude the existence of an atmosphere. Observations of occultations of stars by the moon or the planets tend to the same conclusion. Theoretical astronomy teaches us the distance of the planets from the sun; physics teaches us what quantity of solar light is received by each planet, for given its distance and the length of the revolution with the inclination of the axis, we are led to know the arrangement of the seasons.
Photometry gives us the sum of solar light reflected by the surface of the planet, and thus affords indications relative to certain 'properties of this planetary surface—properties which permit us, for example, to decide with certainty if the light be reflected by a solid surface, such as the planet, or if the rays, not penetrating so far, are sent back in the upper parts of the atmosphere by banks of clouds.
It is the spectrum analysis which furnishes, as we know, the most important auxiliaries, presenting the stars to the eye of the mind just as the microscope reveals infinitely small marvels to the eye of the body.
The luminous rays are messengers, which after having passed through the spectroscope bring us news of the most distant worlds, speaking to us of the calorific intensity of the fixed stars, of metals which are volatilized in their atmosphere, of the incredibly low temperature of the nebulas, and of the gases enveloping the planets.
But it is not my place here to dilate on the spectrum analysis; I only wish to recapitulate briefly and simply what is known of the physical nature of the celestial bodies, and to show that we owe the greater part of our knowledge to the spectroscope.
It is not exaggeration to say that there is no limit to the number of forms in which life manifests itself, and this fact is an argument to those who trust that there are superior beings in the distant world. It shows that directly the primary germs exist there is a possibility of a complete development, and that nature never lacks forms in proportion to the exterior conditions. Thus it is that we have the right to suppose that in Mars there may be creatures with the manifestations of animal life and in the enjoyment of intellectual faculties.
In Mars we can clearly recognize the subdivision of the surface into water and terra firma. Its atmosphere has properties which accord with our own; not only do we certainly find aqueous vapor there, but spectroscopic researches prove that its principal components are the same as those of the terrestrial atmosphere, and that consequently it contains oxygen and nitrogen. Sometimes lines of clouds hide the planet from our view; and sometimes they disappear, to reappear in other places.
The extent of snow and ice covering its poles varies with the seasons. Albeit the temperature of Mars must be sensibly lower than ours from its being farther from the sun, the difference is not considerable enough to be an obstacle
