Wotton written to Lord Bacon in 1620 we learn that Kepler had made himself a portable dark tent fitted with a telescope lens and used for sketching landscapes.
"It appears like the mystical ratios of Kepler which Newton so happily elucidated."
This letter was written two years after Napier's death (of which Kepler was unaware), and in the same year as that in which the Constructio was published.
His astronomical vocation, like that of Kepler, came from without.
Attempts have been made, principally founded on some remarks of Huygens, to show that Descartes had learned the principles of refraction from the manuscript of a treatise by Willebrord Snell, but the facts are uncertain; and, so far as Descartes founds his optics on any one, it is probably on the researches of Kepler.