Concave mirrors, reflected heat, and a bellows to make cold
Optical propositions on light and colour, the burning point of a concave mirror, and cold from converging bellows
A sequence of optical propositions opens the page: an illuminated surface shows its detail to the eye more distinctly than one in shadow, a square mirror throws the sun's image onto a distant object in a round shape, and any white opaque body is partly tinted by the colors facing it. A sketch of a concave mirror f g shows the sun's rays converging pyramidally to a point m, so that a small disk (a b or c d) set in the cone grows hotter the more times it fits into the mirror's surface. The page ends with a specialized toroidal bellows-compressed by two round weights and re-charged by a hand-cranked winch-illustrating Leonardo's claim that just as many rays converging to a point make extreme heat, so many bellows blowing on one point make extreme cold.
On this page
Lit surfaces reveal detail better than shaded ones
The illuminated part of an opaque body sends the image of its details to the eye more discernibly and distinctly than the part found in shadow.
A square mirror reflects the sun in round form
Solar rays striking a square mirror will reflect onto a distant object in a round form.
The burning point of a concave mirror
The sun's heat on the surface of a concave mirror f g comes off it by pyramidal rays converging to a single point m. As many times as that point fits into the mirror's surface, so many times hotter it is; and likewise, as many times as a b or c d fits into the mirror, so many times more powerful is its heat.
A toroidal bellows to make extreme cold
The air cavity is arranged in a ring around a dozen centrally directed nozzles it supplies at once; two large round weights compress the bellows, which recovers its air when lifted by a winch worked with two cranks. Just as many rays converging to one point make extreme heat, many bellows blowing on the same point make extreme cold.
The nature of cold and of air
Cold arises from air that has no heat and from the movement of air. Air of itself is cold and dry, void of matter or vapor, and readily takes on the nature and likeness of whatever touches it-an odor such as musk or sulfur, or the light of a luminous body placed within it.