And in prosecution of this Experiment, having taken the filings of Iron and Steel, and with the point of a Knife cast them through the flame of a Candle, I observed where some conspicuous shining Particles fell, and looking on them with my Microscope, I found them to be nothing else but such round Globules, as I formerly found the Sparks struck from the Steel by a stroke to be, only a little bigger; and shaking together all the filings that had fallen upon the sheet of Paper underneath and observing them with the Microscope, I found a great number of small Globules, such as the former, though there were also many of the parts that had remained untoucht and rough filings or chips of Iron.  So that, it seems, Iron does contain a very combustible sulphureous Body, which is, in all likelihood, one of the causes of this Phaenomenon, and which may be perhaps very much concerned in the business of its hardening and tempering:  of which somewhat it said in the Description of Muscovy-glass.

So that, these things considered, we need not trouble our selves to find out what kind of Pores they are, both in the Flint and Steel, that contain the Atoms of fire, nor how those Atoms come to be hindred from running all out, when a dore or passage in their Pores is made by the concussion:  nor need we trouble our selves to examine by what Prometheus the Element of Fire comes to be fetcht down from above the Regions of the Air, in what Cells or Boxes it is kept, and what Epimetheus lets it go:  Nor to consider what it is that causes so great a conflux of the atomical Particles of Fire, which are said to fly to a flaming Body, like Vultures or Eagles to a putrifying Carcass, and there to make a very great pudder.  Since we have nothing more difficult in this Hypothesis to conceive, first, as to the kindling of Tinder, then how a large Iron-bullet, let fall red or glowing hot upon a heap of Small-coal, should set fire to those that are next to it first:  Nor secondly, is this last more difficult to be explicated, then that a Body, as Silver for Instance, put into a weak Menstruum, as unrectified Aqua fortis should, when it is put in a great heat, be there dissolved by it, and not before; which Hypothesis is more largely explicated in the Description of Charcoal.  To conclude, we see by this Instance, how much Experiments may conduce to the regulating of Philosophical notions.  For if the most Acute Des Cartes had applied himself experimentally to have examined what substance it was that caused that shining of the falling Sparks struck from a Flint and a Steel, he would certainly have a little altered his Hypothesis, and we should have found, that his Ingenious Principles would have admitted a very plausible Explication of this Phaenomenon; whereas by not examining so far as he might, he has set down an Explication which Experiment do’s contradict.