of the copper and lead by the said cupellation; therefore it is justly demanded whence this Encrease proceeds, whether the heat of the fire was not coagulated into a metallick body by means of that melted metal? Therefore it is probable, that if you knew the metallick matrixes in the surface of the earth, in which the beams of the Sun and heat of fire being received, may be coagulated, metals may as well be generated in them, as in the bowels of the earth. But thou repliest it is probable the heat of vulgar fire to have something metallick in it, which comes by attraction of the melted metal in the Cupel, but not in the Sun-beams. He that will thus try the truth, let him put a cupel very well burnt in the beams of the Sun, together with copper and lead, to which let him apply a hollow Looking-glass, so that it may be operated upon by the Sun-beams gathered into a center, and may thence be made hot: But thou must continually hold the Looking-glass in thy hand, that thou maist turn or direct it to the Sun, according to the course thereof, lest the cupel wax cold, the beams of the Sun being turned away, but if it be rightly observed, the work shall be done no less than in a furnace of fire with glowing heat. You must have a Looking-glass at least in diameter two feet, nor must it be too deep; but be in depth the 18 or 20 part of the globe, that so it may the further cast the beams: it must be very artificially smoothed, that it may more exactly gather the beams to the center. Now the preparation of these burning-glasses is not of this place, but in the fourth part of our Furnaces, where we have taught not only how they are to be made of metals, but also of glass, and how polisht and used.