De cometis

the mixing of the air with foreign substances, and the alterations of all those things which the air supports. They also signify convocations held, confederations, seditions, wars, slaughters, pestilences, the infections or improvements of fruits, friendships, pleasures, dances, justice, and iniquity, and new inventions, and the cultures of foreign things, and many other effects, the beginning and mutation of which are in some way from the air. For all these things are from the star dominating through the generation of comets as from a universal cause, and from the comet as from a more principal elementary particular cause, which bears a greater likeness to the universal cause.

That the significations of comets from site, quantity, duration, rarity, and density are accidental

The signification that is taken from the site is because the accident happening will appear in that part of the world towards which it extends its tail, which is to be understood as experience has taught regarding the part of the firmament which the tail faces. For in the regions and places of that part of the firmament, accidents reach many people. The place of the rising of comets also signifies the things by which or through which accidents happen, and also the place, as Ptolemy intended in the second [book of the] Quadripartitum a foundational astrological text, also according to the star or its rays that were there at the beginning of the generation of the comet. And let it not be understood as the region situated in this difference of the position of the world towards which the tail extends; for a comet always extends its tail towards all kingdoms that are behind it. Thus, with the tail of some comet extended towards the east, would they announce [events] to the kingdoms of the Spanish, or to the Romans, or to the Jerusalemites, or to the Chaldeans, or to the Medes, or to the Indians? For to the Spanish themselves at that time, it would signify nothing, etc. One day, also, the tail of a comet can be turned to all directions of the globe of the world, especially when it is near the arctic pole, in the northern regions, though it itself always faces the same part of the firmament. And where then would the events signified by the comet be announced? But durability and density signify constancy and the durability of the impulse. Thus also the quantity of it and the multitude of its substance and materials similar to it signify the strength, multitude, and vehemence of the impulses. The opposites of the said things signify the contrary to the said things.

On the special significations of single species of comets according to the opinion of the ancient wise men

N. ly

Cloud likely referring to a nebulous or hazy comet of the nature of Venus. It harms kings and powerful men, and men rise up in the world who wish to change ancient laws and bring in new things. And the worst signification of it is from the part of the tail.
Horn a comet shaped like a horn of the nature of Mercury. In the part where its tail has appeared, it signifies the death of kings and wars.
Dawn a comet appearing at dawn or morning-star type, of the nature of Mars. When it has appeared in the east with the head depressed lower, it signifies a paucity of waters, great famine, and burnings by fire, and wars in the land of Babylon, and the Arabs, and Egypt, and this extends even to the parts of the west.