An essay of the great effects of even languid and unheeded motion whereunto is annexed An experimental discourse of some little observed causes of the insalubrity and salubrity of the air and its effects / by the Honourable Robert Boyle ...

To the VIIIth. Chapter.

Observation II.

TO shew that the Suspicion I mention my self, a little be∣fore the end of this Chapter, to have had, that the breaking of the Stones there spoken of might possibly be produc'd or promoted by some im∣pressions, remaining after the strokes employ'd to force the Stones out of their Beds, was not altogether with∣out ground.

I shall here observe, that it need not seem incredible, that faint strokes and attritions may leave more lasting and operative Motions among the Insensible Parts, even of compact and solid Bodies, than one would readily imagine. For I have several times found, sometimes by Observa∣tions designedly made, and some∣times by undesigned Accidents, that, having caus'd somewhat thin Vessels of Glass, especially Urinals, to be di∣ligently

made clean with Sand mixt with Water, to loosen or grate off the foulness that adher'd to the sides of the Vessel; though the Vessels, af∣ter having been thus made clean, did not appear to have receiv'd the least injury, and would continue very in∣tire perhaps for several hours, yet af∣ter that time they would of them∣selves break with noise, and thereby become unserviceable for the future. But though this happen'd to many Urinals, yet, because to more others it did not, it seem'd probable that the dissilition depended chiefly upon the peculiar texture of the Glass in this or that Vessel, whether acquir'd by a mixture of the Ingredients, that was not uniform enough or made in a due proportion; or else by the too hasty refrigeration of the Vessel, es∣pecially if it chanc'd, as is not very unusual, to be cool'd more hastily in one part than another.