Magnalia naturæ, or, The philosophers-stone lately exposed to public sight and scale [electronic resource] : being a true and exact account of the manner how Wenceslaus Seilerus, the late famous projection-maker at the emperours court at Vienna, came by and made away with a very great quantity of pouder of projection by projecting with it before the emperour and a great many witnesses, selling it &c. for some years past / by John Joachim Becher : published at the request, and for the satisfaction of several curious, especially of Mr. Boyl &c.