Micrographia. Robert Hooke
its gravity, it is flatted into an Oval. Quicksilver also which to Glass is more incongruous then Air (and thereby being put into a Glass-pipe, will not adhere to it, but by the more congruous air will be forced to have a very protuberant surface, and to rise higher in a greater then a lesser Pipe) this Quicksilver to clean Metal, especially to Gold, Silver, Tin, Lead, &c. Iron excepted, is more congruous then Air, and will not only stick to it, but have a concave Surface like water, and rise higher in a less, then in a greater Pipe.
In all these Examples it is evident, that there is an extraordinary and adventitious force, by which the globular Figure of the contained heterogeneous fluid is altered; neither can it be imagined, how it should otherwise be of any other Figure then Globular: For being by the heterogeneous fluid equally protruded every way, whatsoever part is protuberant, will be thereby deprest. From this cause it is, that in its effects it does very much resemble a round Spring (such as a Hoop.) For as in a round Spring there is required an additional pressure against two opposite sides, to reduce it into an Oval Form, or to force it in between the sides of a Hole, whose Diameter is less then that of the Spring, there must be a considerable force or protusion against the concave or inner side of the Spring; So to alter this spherical constitution of an included fluid body, there is required more pressure against opposite sides to reduce it into an Oval; and, to press it into an Hole less in Diameter then it self, it requires a greater protrusion against all the other sides, What degrees of force are requisite to reduce them into longer and longer Ovals, or to press them into less and less holes, I have not yet experimentally calculated; but thus much by experiment I find in general, that there is alwayes required a greater pressure to close them into longer Ovals, or protude them into smaller holes. The necessity and reason of this, were it requisite, I could easily explain: but being not so necessary, and requiring more room and time then I have for it at present, I shall here omit it; and proceed to shew, that this may be presently found true, if Experiment be made with a round Spring (the way of making which trials is obvious enough.) And with the fluid bodies of Mercury, Air, &c, the way of trying which, will be somewhat more difficult; and therefore I shall in brief describe it. He therefore that would try with Air, must first be provided of a Glass-pipe, made of the shape of that in the fifth Figure, whereof the side AB, represents a straight Tube of about three foot long, C, represents another part of it, which consists of a round Bubble; so ordered, that there is left a passage or hole at the top, into which may be fastened with cement several small Pipes of determinate cylindrical cavities: as let hollow of
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