The dissolving of silver in AQUA FORTIS, and gold in AQUA REGIA, and not VICE VERSA, would be then perhaps no more difficult to know than it is to a smith to understand why the turning of one key will open a lock, and not the turning of another.

But whilst we are destitute of senses acute enough to discover the minute particles of bodies, and to give us ideas of their mechanical affections, we must be content to be ignorant of their properties and ways of operation; nor can we be assured about them any further than some few trials we make are able to reach.

But whether they will succeed again another time, we cannot be certain.

This hinders our certain knowledge of universal truths concerning natural bodies: and our reason carries us herein very little beyond particular matter of fact.
26.

Hence no Science of Bodies within our reach.
And therefore I am apt to doubt that, how far soever human industry may advance useful and experimental philosophy in physical things, SCIENTIFICAL will still be out of our reach: because we want perfect and adequate ideas of those very bodies which are nearest to us, and most under our command.