Dioptrics

...[things which] are still missing in Aristotle's Meteorology, can be supplied from elsewhere.

I had also thought of adding a small book here about the Rainbow; it would have been a supplement to Aristotle’s inquiry on the rainbow, but the true causes of Sun Dogs original: "Pareliorum"; also known as "mock suns," these are bright spots that appear on either side of the sun due to ice crystals in the atmosphere. were still missing, and these are intertwined with the causes of ominous rainbows. Therefore, for the time being, I have set this task aside.

Since the science of Optics benefits natural philosophy so much, Pena is quite right to expect even more from optics—in Porphyrian Referring to Porphyry (c. 234 – c. 305 AD), a Neoplatonic philosopher whose works often blended philosophy, theology, and theurgy. magic and theology, and in the debunking of sleight-of-hand tricks. Nor does Giambattista della Porta’s Natural Magic A popular 16th-century work that explored various scientific and pseudo-scientific wonders. promise little; let the reader consult it, and he will see that the discipline of optics provides marvelous uses throughout all of human life.

Thus far, then, let Pena be heard by us, concluding his very learned speech on the excellence of Optics and its astounding effects in uncovering the nature of things.

Now it is time for me to keep my promises and show that, through this branch of optics which we call Dioptrics The study of the refraction of light through lenses, as opposed to "Catoptrics," which deals with mirrors. and its subject, Spyglasses original: "Perspicillis"; here Kepler refers to the telescope, which was a very recent invention., we have learned far more marvelous things about the nature of reality in a short span of time—so much so, indeed, that everything we have produced so far from Pena via the benefit of optics might seem like child's play.

Everyone is currently reading Galileo’s Starry Messenger, as well as my own modest Conversation Kepler's Dissertatio cum Nuncio Sidereo (1610), written in response to Galileo's discoveries. with that messenger, and also my brief Narration confirming the Starry Messenger. Therefore, let the reader briefly weigh the main points of that Messenger, considering what great things were discovered by the benefit of that spyglass—the principles of which I demonstrate in this very book. Sight testified that there was a certain bright body in the sky which we call the Moon; it was demonstrated through optical principles that this body is spherical. Astronomy, through various reasonings built upon optical foundations, had even established its distance from the Earth as roughly sixty Earth-radii. Various spots used to appear on that body, and there followed the obscure opinion of a few philosophers—introduced by Hecataeus Hecataeus of Abdera, a Greek historian of the 4th century BC. into the myths about the island of the Hyperboreans In Greek mythology, a legendary people who lived in a land of perpetual sunshine in the far north.—of mountains and valleys, of moisture and