Gal II 108 a

H 15 512
Petrus de Valetia, Physician of Zurich, was the author of this treatise as it seems, for in the Library of Zurich it is attributed to him, as testified by Rod. Amm.

Treatise of a Physician of Zurich on Comets. Begins a preface

Aristotle said: "No one is a good judge of things they do not know." Experts in many sciences and arts, by proving these things, affirm that all natural events and most voluntary ones are initiated and directed by celestial influences. Aristotle says: "Since this world is necessarily contiguous to the upper regions, all its power is governed from there." Therefore, the ignorant should reveal their follies by speaking without biting i.e., without malice or attacking others, so that their own ignorance and stupidity do not become clear. And even if they appear learned in some things, they are ignorant of those things of which they cannot be judges. But I shall confirm myself in speaking about comets using the words and opinions of those who have studied the writings of the wise with a clear intellect. But because among many teaching doctrines and disciplines, an opinion has prevailed and a conviction has been induced in the common people that it is superstitious and reckless to believe that astronomical configurations and the appearances of comets are the causes of wars, friendships, sects, and the alteration of laws, and that these things should also be subject to free will; yet they cannot deny that these are causes of natural effects, as daily experience, which teaches the common people more than the philosophers of our time, continuously shows. It would therefore be a vain and ridiculous story to speak of such events, unless they were induced and certified in philosophy, taught by manifest persuasions, so that the aforementioned belief is not superstitious, but founded on astronomical influences. Wherefore, in speaking of the significations of the comet, I shall first present a universal discourse. There will be two parts to what is to be said. Here follow the chapters of this treatise

The first part is the universal discourse. First chapter

1 On the kinds of comets 2 chapter 2 On the generation of comets
3 An introduction of some things by whose similarity the substances of comets receive their properties and natures from the heavens. 8
How the celestial virtue is acquired by cometary substances and similar things, similar to the seminal force.
4 On the motion of comets 6 5 On the figure, color, and size of comets
7 An enumeration of the individual species of comets as determined by the ancients.
8 On the knowledge of comets a posteriori or "that it is." 9
10 On the knowledge of comets a priori or "the reason why." 11 How the substances of comets and similar things have the power to change bodies and spirits and to induce sickness and mortality. 12 How comets cause sudden death.
13 How the cognitive power is changed by the substances of comets and things similar to them.
18 How new laws and customs arise from new inclinations and morals, and how old ones are abrogated. 14
How sects, prophets, and the cultivation of foreign things arise.
16 How the effects of comets and astronomical applications last for many years after they have passed.
17 How some effects do not last a long time after the appearance of comets.
18 A summary of all that has been said. 19 On the ways in which comets signify.
20 On the signification of comets according to their position, quantity, duration, rarity, and density.
21 On the special significations of the individual species of comets according to the opinion of ancient wise men. 22 A summary and order of the significations of comets.