He already knew of the phenomenon, which is insufficiently explained even in our day, that during the phases of greatest visibility of Venus the dark side appears to have a faint luminosity. “The simplest explanation to give of this,” he says, “is that at the epochs when this faint light on Venus is visible, the inhabitants of the planet organise festivals and general illuminations, which are the easier to arrange on account of the vegetations of Venus being incomparably more luxuriant than even the virgin forests of Brazil. These festivals are probably celebrated on the occasion of political changes or according to religious periods. Now, the principal observations of the ashen light on Venus are those of Mayer in 1759 and of Harding in 1806.” Whence he draws the following conclusion: “Between the observation of Mayer and that of Harding 76 years of Venus and 47 Earth years have elapsed. If this period has a religious character, we cannot see a justification for that number of years, but it becomes more comprehensible if we assume that some Alexander or Napoleon then attained universal power. If we assume that the ordinary life of an inhabitant of Venus lasts 130 years of Venus, which amount to 80 terrestrial years, the reign of such an autocrat could easily last 76 years as reckoned on Venus. I have no intention to press this opinion and do not claim its credibility, even should it appeal to the reader’s imagination; but if my hypothesis is correct, we at least receive direct testimony to the existence of inhabitants on Venus. Even if the period were shorter, the phenomenon might still be due to some other observance. One could celebrate all the great festivals by similar illuminations which would sometimes follow close upon one another. The fires would serve another purpose, inasmuch as they would thin out the forests and provide fresh arable ground for an increasing population. Large migrations of people would be prevented, and the consequent wars would be avoided and the race would remain united.”
One must acknowledge that these ideas of Gruithuisen are most fantastic. I have frequently observed this unilluminated hemisphere of Venus, notably in September 1895 and in April 1897: it appeared to me of a violet colour, and the idea of illuminations by the inhabitants is pure romance.
He also then passes in review the ideas of Kant which one finds expounded in the two works cited above and which therefore I need not quote. We know that for the Philosopher of Königsberg the intelligence and the degree of perfection of the inhabitants of the planets is in proportion to their distance from the sun.
We may add to the remarks of M. Scheiner that the writers who have dealt with the question of the plurality of worlds have nearly all judged the planets from the appearances they present to us from our point of observation, and have assumed the harmony of nature according to the manner of Bernardin de St. Pierre. For this occasion I have re-read his hook with some interest. To this very simple member of the Institut, Venus is a bright world peopled by amorous natives “who give themselves up to dance, festivals, and songs, or compete for swimming prizes, like the happy islands of Tahiti”; the inhabitants of Mars are warlike, “resembling the northern Germans, their forests and hills, their atmosphere resounding to the warlike sound of their horns and that of drums and trumpets which announce the spilling of blood”; on Jupiter “they resemble the Dutch, being industrious, patient, wise, reflective, and tending their numerous herds in their vast fields,” etc., etc.
The author of Paul et Virginie remains purely terrestrial in these descriptions, which he believes to be astronomical.
But let us return to the dissertation of M. Scheiner. He passes on to the purely scientific aspect of the question, which is the only one which interests us here.
THE ORIGIN OF LIFE
The problem of knowing if worlds other than the Earth, being habitable, are really inhabited, depends really upon this question: How did life appear on this Earth?
It is irrefutable that there was a time when the Earth was not habitable in the usual sense. Therefore life necessarily had a commencement. “This can have taken place in three different ways, either by a special act of creation, in which case it is of little importance to our problem to know whether this act was accomplished in a complete manner as taught by the Bible or whether it was limited to the creation of the inferior forms of life; or by spontaneous generation; or, lastly, by the importation from space, in which we can just as well imagine germs of life as gases and inorganic substances.
“From the philosophical point of view, these three hypotheses are equally well-founded, for none is more easily conceived than the other and observation has not yet confirmed any of them.