One Experiment, which does very much illustrate my present Explication, and is in it self exceeding pretty, I must not pass by: And that is a way of making small Globules or Balls of Lead, or Tin, as small almost as these of Iron or Steel, and that exceeding easily and quickly, by turning the filings or chips of those Metals also into perfectly round Globules. The way, in short, as I received it from the Learned Physitian Doctor I.G. is this;
Reduce the Metal you would thus shape, into exceeding fine filings, the finer the filings are, the finer will the Balls be: Stratifie these filings with the fine and well dryed powder of quick Lime in a Crucible proportioned to the quantity you intend to make: When you have thus filled your Crucible, by continual stratifications of the filings and powder, so that, as neer as may be, no one of the filings may touch another, place the Crucible in a gradual fire, and by degrees let it be brought to a heat big enough to make all the filings, that are mixt with the quick Lime, to melt, and no more; for if the fire be too hot, many of these filings will joyn and run together; whereas if the heat be proportioned, upon washing the Lime-dust in fair Water, all those small filings of the Metal will subside to the bottom in a most curious powder, consisting all of exactly round Globules, which, if it be very fine, is very excellent to make Hour-glasses of.
Now though quick Lime be the powder that this direction makes choice of, yet I doubt not, but that there may be much more convenient ones found out, one of which I have made tryal of, and found very effectual; and were it not for discovering, by the mentioning of it, another Secret, which I am not free to impart, I should have here inserted it.
Observ. [IX]. Of the Colours observable in Muscovy-Glass, and other thin Bodies.
Moscovy-glass, or Lapis specularis, is a Body that seems to have as many Curiosities in its Fabrick as any common Mineral I have met with: for first, It is transparent to a great thickness: Next, it is compounded of an infinite number of thin flakes joyned or generated one upon another so close & smooth, as with many hundreds of them to make one smooth and thin Plate of a transparent flexible substance, which with care and diligence may be slit into pieces so exceedingly thin as to be hardly perceivable by the eye, and yet even those, which I have thought the thinnest, I have with a good Microscope found to be made up of many other Plates, yet thinner; and it is probable, that, were our Microscopes much better, we might much further discover its divisibility. Nor are these flakes only regular as to the smoothness of their Surfaces, but thirdly, In many Plates they may be perceived to be terminated naturally with edges of the figure of a Rhomboeid. This Figure is much more conspicuous in our English talk, much whereof is found in the Lead Mines, and is commonly called Spar, and Kauck, which is of the same kind of substance with the Selenitis, but is seldom found in so large flakes as that is, nor is it altogether so tuff, but is much more clear and transparent, and much more curiously shaped, and yet may be cleft and flak’d like the other Selenitis. But fourthly, this stone has a property, which in respect of the Microscope, is more notable, and that is, that it exhibits several appearances of Colours, both to the naked Eye, but much more conspicuously to the Microscope; for the exhibiting of which, I took a piece of Muscovy-glass, and splitting or cleaving it into thin Plates, I found that up and down in several parts of them I could plainly perceive several white specks or flaws, and others diversly coloured with all the Colours of the Rainbow; and with the Microscope I could perceive, that these Colours were ranged in rings that incompassed the white speck or flaw, and were round or irregular, according to the shape of the spot which they terminated; and the position of Colours, in respect of one another, was the very same as in the Rainbow. The consecution of those Colours from the middle of the spot outward being Blew, Purple, Scarlet, Yellow, Green; Blew, Purple, Scarlet, and so onwards, sometimes half a score times repeated, that is, there appeared six, seven, eight, nine or ten several coloured rings or lines, each incircling the other, in the same manner as I have often seen a very vivid Rainbow to have four or five several Rings of Colours, that is, accounting all the Gradations between Red and Blew for one: But the order of the Colours in these Rings was quite contrary to the primary or innermost Rainbow, and the same with those of the secondary or outermost Rainbow; these coloured Lines or Irises, as I may so call them, were some of them much brighter then others, and some of them also very much broader, they being some of them ten, twenty, nay, I believe, neer a hundred times broader then others; and those usually were broadest which were neerest the center or middle of the flaw. And oftentimes I found, that these Colours reacht to the very middle of the flaw, and then there appeared in the middle a very large spot, for the most part, all of one colour, which was very vivid, and all the other Colours incompassing it, gradually ascending, and growing narrower towards the edges, keeping the same order, as in the secundary Rainbow, that is, if the middle were Blew, the next incompassing it would be a Purple, the third a Red, the fourth a Yellow, &c. as above; if the middle were a Red, the next without it would be a Yellow, the third a Green, the fourth a Blew, and so onward. And this order it alwayes kept whatsoever were the middle Colour.
There was further observable in several other parts of this Body, many Lines or Threads, each of them of some one peculiar Colour, and those so exceedingly bright and vivid, that it afforded a very pleasant object through the Microscope. Some of these threads I have observed also to be pieced or made up of several short lengths of differently coloured ends (as I may so call them) as a line appearing about two inches long through the Microscope, has been compounded of about half an inch of a Peach colour, ⅛ of a lovely Grass-green, ¾ of an inch more of a bright Scarlet, and the rest of the line of a Watchet blew. Others of them were much otherwise coloured; the variety being almost infinite. Another thing which is very observable, is, that if you find any place where the colours are very broad and conspicuous to the naked eye, you may, by pressing that place with your finger, make the colours change places, and go from one part to another.
There is one Phænomenon more, which may, if care be used, exhibit to the beholder, as it has divers times to me, an exceeding pleasant, and not less instructive Spectacle; And that is, if curiosity and diligence be used, you may so split this admirable Substance, that you may have pretty large Plates (in companion of those smaller ones which you may observe in the Rings) that are perhaps an ⅛ or a ⅙ part of an inch over, each of them appearing through the Microscope most curiously, intirely, and uniformly adorned with some one vivid colour: this, if examined with the Microscope, may be plainly perceived to be in all parts of it equally thick. Two, three, or more of these lying one upon another, exhibit oftentimes curious compounded colours, which produce such a Compositum, as one would scarce imagine should be the result of such ingredients: As perhaps a faint yellow and a blew may produce a very deep purple. But when anon we come to the more strict examination of these Phænomena, and to inquire into the causes and reasons of these productions, we shall, I hope, make it more conceivable how they are produced, and shew them to be no other then the natural and necessary effects arising from the peculiar union of concurrent causes.
These Phænomena, being so various, and so truly admirable, it will certainly be very well worth our inquiry, to examine the causes and reasons of them, and to consider, whether from these causes demonstratively evidenced, may not be deduced the true causes of the production of all kind of Colours. And I the rather now do it, instead of an Appendix or Digression to this History, then upon the occasion of examining the Colours in Peacocks, or other Feathers, because this Subject, as it does afford more variety of particular Colours, so does it afford much better wayes of examining each circumstance. And this will be made manifest to him that considers, first, that this laminated body is more simple and regular then the parts of Peacocks feathers, this consisting only of an indefinite number of plain and smooth Plates, heaped up, or incumbent on each other. Next, that the parts of this body are much more manageable, to be divided or joyned, then the parts of a Peacocks feather, or any other substance that I know. And thirdly, because that in this we are able from a colourless body to produce several coloured bodies, affording all the variety of Colours imaginable: And several others, which the subsequent Inquiry will make manifest.
To begin therefore, it is manifest from several circumstances, that the material cause of the apparition of these several Colours, is some Lamina or Plate of a transparent or pellucid body of a thickness very determinate and proportioned according to the greater or less refractive power of the pellucid body. And that this is so, abundance of Instances and particular Circumstances will make manifest.