Micrographia, by Robert Hooke

Observ. v. Of watered Silks, or Stuffs.

There are but few Artificial things that are worth observing with a Microscope, and therefore I shall speak but briefly concerning them. For the Productions of art are such rude mis-shapen things, that when view'd with a Microscope, is little else observable, but their deformity. The most curious Carvings appearing no better then those rude Russian Images we find mention'd in Purchas, where three notches at the end of a Stick, stood for a face. And the most smooth and burnish'd surfaces appear most rough and unpolisht: So that my first Reason why I shall add but a few observations of them, is, their mis-shapen form; and the next, is their uselessness. For why should we trouble our selves in the examination of that form or shape (which is all we are able to reach with a Microscope) which we know was design'd for no higher a use, then what we were able to view with our naked eye? Why should we endeavour to discover mysteries in that which has no such thing in it? And like Rabbins find out Caballisms, and ænigmâs in the Figure, and placing of Letters, where no such thing lies hid: whereas in natural forms there are some so small, and so curious, and their design'd business so far remov'd beyond the reach of our sight, that the more we magnify the object, the more excellencies and mysteries do appear; And the more we discover the imperfections of our senses; and the Omnipotency and Infinite perfections of the great Creatour. I shall therefore onely add one or two Observations more artificial things, and then come to the Treaty concerning such matters as are the Productions of a more curious Workman. One of these, shall be that of a piece of water'd Silk, Schem. 3.
Fig. 2.
represented in the second Figure of the third Scheme, as it appear'd through the least magnifying Glass. AB signifying the long way of the Stuff, and CD the broad way. This Stuff, if the right side of it be looked upon, appears to the naked eye, all over so waved, undulated, or grain'd, with a curious, though irregular variety of brighter and darker parts, that it adds no small gracefulness to the Gloss of it. It is so known a propriety, that it needs but little explication, but it is observable, which perhaps everyone has not considered, that those parts which appear the darker part of the wave, in one position to the light, in another appears the lighter, and the contrary; and by this means the undulations become transient, and in a continual change, according as the position of the parts in respect of the incident beams of light is varied. The reason of which odd phænomena, to one that has but diligently examin'd it even with his naked eye, will be obvious enough. But he that observes it with a Microscope, may more easily perceive what this Proteus is, and how it comes to change its shape. He may very easily perceive, that it proceeds onely from the variety of the Reflections of light, which is caus'd by the various shape of the Particles, or little protuberant parts of the thread that compose the surface; and that those parts of the waves that appear the brighter, throw towards the eye a multitude of small reflections of light, whereas the darker scarce afford any. The reason of which reflection, the Microscope plainly discovers, as appears by the Figure. In which you may perceive, that the brighter parts of the surface consist of an abundance of large and strong reflections, denoted by a, a, a, a, a, &c. for the surfaces of those threads that run the long way, are by the Mechanical process of watering, creas'd or angled in another kind of posture then they were by the weaving: for by the weaving they are onely bent round the warping threads; but by the watering, they are bent with an angle, or elbow, that is in stead of lying, or being bent round the threads, as in the third Figure, a, a, a, a, a, are about b, b, b (b, b, b representing the ends, as 'twere, of the cross threads, they are bent about) they are creas'd on the top of those threads, with an angle, as in the fourth Figure, and that with all imaginable variety; so that, whereas before they reflected the light onely from one point of the round surface, as about c, c, c, they now when water'd, reflect the beams from more then half the whole surface, as de, de, de, and in other postures they return no reflections at all from those surfaces. Hence in one posture they compose the brighter parts of the waves, in another the darker. And these reflections are also varied, according as the particular parts are variously bent. The reason of which creasing we shall next examine; and here we must fetch our information from the Mechanism or manner of proceeding in this operation; which, as I have been inform'd, is no other then this.

They double all the Stuff that is to be water'd, that is, they crease it just through the middle of it, the whole length of the piece, leaving the right side of the Stuff inward, and placing the two edges, or silvages just upon one another, and, as near as they can, place the wale so in the doubling of it, that the wale of the one side may lie very near parallel, or even with the wale of the other; for the nearer that posture they lie, the greater will the watering appear; and the more obliquely, or across to each other they lie, the smaller are the waves. Their way for folding it for a great wale is thus: they take a Pin, and begin at one side of the piece in any wale, and so moving it towards the other side, thereby direct their hands to the opposite ends of the wale, and then, as near as they can, place the two opposite ends of the same wale together, and so double, or fold the whole piece, repeating this enquiry with a Pin at every yard or two's distance through the whole length; then they sprinkle it with water, and fold it the longways, placing between every fold a piece of Pastboard, by which means all the wrong side of the water'd Stuff becomes flat, and with little wales, and the wales on the other side become the more protuberant; whence the creasings or angular bendings of the wales become the more perspicuous. Having folded it in this manner, they place it with an interjacent Pastboard into an hot Press, where it is kept very violently prest, till it be dry and stiff; by which means, the wales of either contiguous sides leave their own impressions upon each other, as is very manifest by the second Figure, where 'tis obvious enough, that the wale of the piece ABCD runs parallel between the pricked lines ef, ef, ef, and as manifest to discern the impressions upon these wales, left by those that were prest upon them, which lying not exactly parallel with them, but a little athwart them, as is denoted by the lines of, oooo, gh, gh, gh, between which the other wales did lie parallel; they are so variously, and irregularly creas'd that being put into that shape when wet, and kept so till they be drie, they so let each others threads, that the Moldings remain almost as long as the Stuff lasts.

Hence it may appear to any one that attentively considers the Figure, why the parts of the wale a, a, a, a, a, a, should appear bright; and why the parts b, b, b, b, b, b, b, should appear shadowed, or dark; why some, as d, d, d, d, d, d, should appear partly light, and partly dark: the varieties of which reflections and shadows are the only cause of the appearance of watering in Silks, or any other kind of Stuffs.

From the variety of reflection, may also be deduc'd the cause why a small breez or gale of wind ruffling the surface of a smooth water, makes it appear black; as also, on the other side, why the smoothing or burnishing the surface of whitened Silver makes it look black; and multitudes of other phænomena might hereby be solv'd, which are too many to be here insisted on.

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Last updated Monday, March 17, 2014 at 16:42