We took a Leaf of Such Foliated Gold as Apothecaries are wont to Gild their Pills with; and with the Edge of a Knife, (lightly moysten'd by drawing it over the Surface of the Tongue, and afterwards) laid upon the edge of the Gold Leaf; we so fasten'd it to the Knife, that being held against the light, it conctinu'd extended like a little Flagg. This Leaf being held very near the Eye, and obverted to the Light, appear'd so full of Pores, that it seem'd to have such a kind of Transparency as that of a Sive, or a piece of Cyprus, or a Love-Hood; but the Light that pass'd by these Pores was in its Passages So Temper'd with Shadow, and Modify'd, that the Eye discern'd no more a Golden Colour, but a Greenish Blew. And for other's satisfaction, we did in the Night look upon a Candle through such a Leaf of Gold; and by trying the Effect of Several Proportions of Distance betwixt the Leaf, the Eye and the Light, we quickly hit upon such a Position for the Leaf of Gold, as that the flame, look'd on through it, appear'd of a Greenish Blew, as we have seen in the Day time. The like Experiment try'd with a Leaf of Silver succeeded not well. * * * * * _EXPERIMENT X._ We have sometimes found in the Shops of our Druggists, a certain Wood, which is there called _Lignum Nephriticum_, because the Inhabitants of the Country where it grows, are wont to use the Infusion of it made in fair Water against the Stone of the Kidneys, and indeed an Eminent Physician of our Acquaintance, who has very Particularly enquir'd into that Disease, assures me, that he has found such an Infusion one of the most effectual Remedyes, which he has ever tried against that formidable Disease. The ancientest Account I have met with of this Simple, is given us by the Experienc'd _Monardes_ in these Words. _Nobis,_ says he,[16] _Nova Hispania mittit quoddam ligni genus crassum & enode, cujus usus jam diu receptus fuit in his Regionibus ad Renum vitia & urinæ difficultates ac arenulas pellendas. Fit autem hac ratione, Lignum assulatim & minutim concisum in limpidissima aqua fontana maceratur, inque ea relinquitur, donec aqua à bibentibus absumpta sit, dimidia hora post injectum lignum aqua cæruleum colorem contrabit, qui sensim intenditur pro temporis diuturnitate, tametsi lignum candidum fit_. This Wood, _Pyrophilus_, may afford us an Experiment, which besides the singularity of it, may give no small assistance to an attentive Considerer towards the detection of the Nature of Colours. The Experiment as we made it is this. Take _Lignum Nephriticum_, and with a Knife cut it into thin Slices, put about a handfull of these Slices into two three or four pound of the purest Spring-water, let them infuse there a night, but if you be in hast, a much shorter time may suffice; _decant_ this Impregnated Water into a clear Glass Vial, and if you hold it directly between the Light and your Eye, you shall see it wholly Tincted (excepting