DIALOGO PRIMO

heads: one of which is that lauded repugnance that nature has toward admitting a vacuum: for the other, it is necessary (this of the Vacuum not being enough) to introduce some glue, viscous substance, or paste that tenaciously connects the particles of which that body is composed. I will speak first of the Vacuum, showing with clear experiences what and how great its virtue is. And first, the sight—whenever it pleases us—of two plates of marble, metal, or glass, exquisitely smoothed, cleaned, and polished, such that when one is placed upon the other, it moves above it sliding without any effort (a certain argument that no glue joins them), but wanting to separate them while keeping them equidistant, such a repugnance is found that the upper one lifts and pulls the other along with it, and perpetually keeps it suspended, even though it is very thick and heavy. This evidently shows us nature's horror at having to admit—if even for a brief moment of time—the empty space that would remain between them before the rush of the parts of the surrounding air had occupied and filled it. It is also seen that, even if such two plates were not exactly clean and therefore their contact was not entirely exquisite, in wishing to separate them slowly no resistance is found other than that of gravity alone. However, in a sudden lifting, the lower stone is lifted, but immediately falls, following the upper one only for that very brief time which is sufficient for the dissipation of that little bit of air which was interposed between the plates, which did not mate well, and for the entry of the other surrounding air. Such resistance, which is so sensibly perceived between the two plates, cannot be doubted to reside equally between the parts of a solid, and that in their attachment it enters at least in part, and as a concomitant cause.

Sagr. Stop, I pray you, and grant me that I may state a particular consideration that has just fallen into my mind: and this is that seeing how the lower plate follows the upper one, and that it is lifted with very fast motion, makes us certain that, contrary to the statement of many philosophers—perhaps of Aristotle himself—motion in a vacuum would not be instantaneous; because if it were such, the named two plates