Namque uti aeneum vas non in summis labris plenum sed aquae mensurae suae capacitatis habens tribus duas partes operculumque in eo conlocatum, cum ignis vehe-menti fervore tangatur, percalefieri cogit aquam, ea autem propter naturalem raritatem in se recipiens fervoris validam inflationem non modo implet vas, sed spiritibus extollens operculum et crescens abundat, sublato autem operculo emissis inflationibus in aere patenti rursus ad suum locum residit: ad eundem modum ea capita fontium cum sunt angustiis conpressa, ruunt in summo spiritus aquae bullitus, simul autem sunt latius aperti, exanimati per raritates liquidae potestatis residunt et restituuntur in libramenti proprietate.
For instance, let a bronze vessel be filled not to the brim but holding two-thirds, by measure, of its capacity of water; and let a lid be placed upon it. When it is subjected to the vehement heat of the fire, it makes the water boil. Yet, owing to its natural penetrability, it takes up a strong inflation of the heat, and not only fills the vessel but, raising the lid with the currents of air, it expands and boils over. When, however, the lid is removed, the steam passes into the open and the water settles down into its own place again. In the same way when fountain-heads are forced along narrow channels, the currents of air rush in bubbles through the water on the top; as soon as the channels are opened out wider, the springs part with the air through the pores of the liquid potency, and, settling down, they regain their proper level.
final_alignments\Vitruvius_Architecture_Book_8.json