Excerpted from De Impressionibus Elementorum

As Jacob testifies in his canon, "everything given from above is best and every gift that comes from the father of light is perfect, around whom there is no transmutation, nor shadow of change." It is necessary, moreover, for this to happen without mediation in certain circumstances and, in some circumstances, with mediation. Therefore philosophers, even if they do not completely understand the matter, nevertheless they must not ignore the natures of things, and not ignoring the rays descending from supercelestial bodies over corporeal bodies to offer the greatest cause of their transformation, they say that the rays are reflected and condensed in order to generate heat for us. The sign of which is that in valleys, the heat is greater than in mountainous areas. As a result, snow remains longer in mountainous areas than in valleys. Snow even remains in certain ones of the highest mountain ranges perpetually.

original latin

Hoc habito manifestum est quod radii in aquis descendunt ad fundum, cum aqua sit corpus transparens sicut a¨er, cornuglacies et vitrum. In fundis ergo aquarum est reflexio, quare maior est calor in fundo quam in superficie.

Si autem quaerat quis quare aqua multum frigefacta congelatur, cum frigiditas sit eius naturalis potentia, similiter et humiditas ut videtur et fluxibilitas, ad hoc respondendum est quod omnis aqua naturaliter est frigida sed non fluida, immo potius ex natura sua est congelata.

Sed cum natura a¨eris non sit esse sub aqua, ascendit super aquam; ascendit autem in ampulla ex ipsa aqua. Multae autem ampullae, cum ascendunt super aquam, simul se tenent per naturam humiditatis ampullarum et ex illis fit vapor vel fumus, ex quibus fiunt nubes.

Et nota quod generatio pluviae et roris differunt secundum magnum et parvum et secundum diversa loca generationis. Cum vero ascendit nubes ad secundum interstitium, fit major abstractio caloris et destruuntur ampullae penitus a calore successive tantum, quare molle est quod relinquitur sicut lana et fit nix. Si autem subito deferatur nubes sursum ad secundum interstitium, subito destruitur a calore et fit lapis rotundus et est generatio grandinis, sicut ampulla fuit rotunda.