Knutzen himself was apparently rather unconcerned about such criticism. Even his book on the topic, Vernünftige Gedanken von den Cometen, darinnen deren Natur und Beschaffenheit nebst der Art und Ursachen ihrer Bewegung untersuchet und vorgestellet, auch zugleich eine kurze Beschreibung von dem merkwürdigen Cometen deß jetztlauffenden Jahres mitgetheilet wird, has no indication of Knutzen even considering such a possibility. Knutzen’s motivation for his book, beyond introducing the comet of 1744 to a wider audience, is to criticise superstitious ideas where comets are regarded as harbingers of doom.
This motive lies even behind Knutzen’s more questionable thoughts, like the false identification of the 1744 comet. Knutzen emphasises the regularity of the comet’s movement, as a guarantee that they are natural phenomena. He uses a simple induction to justify the assertion that comets continue to move with the same regularity as they have appeared to do - it is equally justifiable, Knutzen says, as when Adam noted after a few days that the sun will always rise in the morning. Such regularity statements seem the more justified, the shorter the time between two appearances. Thus, Knutzen is very eager to show that 1744 comet was the same as had been seen a couple of years ago. This leads him to insist more generally that there are less comets in our solar system than other astronomers and even Newton had assumed - seemingly different comets have often been just appearances of one comet, seen in different parts of the sky due to slight changes in the comet’s orbit, crossing Earth’s ecliptic at different points at different times.
Knutzen’s main point against taking comets as omens is based on showing a failure of another inductive move. Knutzen notes that if comets were such omens or signs of bad events, they would either be causally connected to such events or then the connection would have to be an effect of God’s arbitrary choice, similar to when he in the Bible sets up rainbow as a sign of his promise to not flood the world again. Knutzen then points out that neither possibility really works. If God had set comets as an arbitrary sign, he would have had to teach this sign to us, either through revelation or through experience. There’s no mention of such a sign in the Bible - in fact, the book even speaks against looking at such astrological signs. Even experience speaks against this - if God had meant comets as arbitrary signs of bad things, then he surely would have meant them especially as a sign for astronomers, who are most certain to see these omens, but astronomers who have found most comets have not been particularly unlucky.
Similarly, Knutzen shows that there seems to be no natural connection between comets and bad events. Undoubtedly sometimes comets have appeared during a time when a war has been going on or some king has died or some other calamity has fallen upon some country. Indeed, since Earth is big, it is almost inevitable that some type of disaster is almost always going on at some point of the globe. If a comet would have some noticeable effect on the earthly goings-on, it would have to be a global effect, but there’s no correlation between global crises and appearance of comets. In fact, Knutzen continues, there’s no clear causal mechanism by which a comet could influence such events. For instance, suppose someone would say that comets could cause wars by having a force to aggravate people. Problem is, such a force would not just cause wars, but Hobbesian chaos, where everyone attacked everyone else. If comets would cause only wars, then such a force would have to affect only royalty, but it is unclear how and why such a lifeless and unconscious object as comet could pick out kings and queens as its target.
In his wish to show that comets have not harmed Earth in any manner, Knutzen goes a bit too far and insists that comets could never have an adverse effect on Earth, discounting even the notion that a comet could hit the Earth or at least fly so close that its gravity might cause some disturbances. Thus, Knutzen discounts the worries of his contemporary, William Whiston, who had suggested that such catastrophic meetings had indeed occurred before - Jewish tradition told that Noah had seen a comet before the flood, which Whiston saw as a sign of the mythical flood being an effect of a watery comet hitting Earth. Knutzen was convinced that this tale was just yet another coincidence, and since comets had never hit Earth, they would not hit it in the future. Then again, he suggested that the Jewish tradition might explain historically why comets were universally feared: Noah associated for the rest of his life comets with disasters and taught his descendants to also do so.
Although Knutzen did not then believe in comets as divine signs, he did speculate on their having some purpose in the divine plans. Comets, Knutzen deduced, are just like planets in being mostly solid objects, surrounded by an atmosphere formed from gases and dust. The main difference with the regular planets is that the orbit of comets is very oblong and so a comet is sometimes very close to the Sun, sometimes very far away from it. When the comet approaches the Sun, the increasing gravity and the heat make the comet’s atmosphere appear as a tail. When the comet again changes its course to the outer reaches of the Solar System, it still retains some of its heat - and perhaps, Knutzen suggests, the whole purpose of a comet doing such a trip is to transfer some of this heat to where it wouldn’t otherwise get.
Next time, we shall once again return to Wolff's account of natural law.
