To do this, a frame A ([Plate 50], [fig. 2]) holds the Mirror; and this frame has a horizontal motion round the post B, something like a common windmill. In this frame and on two horizontal trunnions, turns the Mirror C D: and one or both these trunnions are hollow, to admit of a process we shall shortly mention. This Mirror itself is composed of an air-tight ring C D, of a width proportionate to the diameter adopted; and on which are fixed two heads, much like those of a tambourine, (or the under head might be made of some metallic substance). The head a b c, is made of a fine texture, duly prepared and varnished till it becomes air tight, and then there are stuck to it, a number of small hexagonal looking-glasses or mirrors of any kind, (see [fig. 7]) which thus fill up the whole space, and prepare the Mirror for the intended change of form. The method of giving this form, consists in exhausting, more or less, this tambourine of air, when, by the pressure of the atmosphere, the heads will take the form a b c, that is a spherically concave form—fit to reflect the sun’s rays as correctly as this our object requires; and thus may some thousand small images of the sun be brought to fall on the same spot, and an immense heat be occasioned. The accounts we have of the destruction of the Roman fleet by the united mirrors of Archimedes, make this process appear the more feasible—as whatever were the methods of uniting the foci of his mirrors, a similar effect may be expected from this simple process.
My readers will perceive that this Machine has the advantages of the universal joint, by which it can be directed to the sun in every position; and even made to fix his ardours on any immoveable spot for a good length of time. The persons to whom I particularly address these ideas, will require no further details to conceive the less obvious circumstances of this Invention. In general, we want no effect that requires optical precision: but if we did, it could be obtained to a good degree, by methods similar to these.
I shall only add here, that this [fig. 2] is given as a section—because intended to represent a parallelogram, as well as a solid of revolution: and thus (with proper mirrors) to make what now appears a spherical focus, a linear one—fit to heat a cylindrical vessel with it’s contents; and thereby draw power from the sun’s heat, without running expense. I am serious when I say, that we can thus, practically, collect the solar rays which fall on many hundred square feet of surface; and produce by them, at any desired distance, effects to which those obtained from modern burning mirrors, are but as sparks to a blaze.
OF
AN ENGRAVING MACHINE,
For large Patterns.
This Machine supposes at once a new kind of engraving, and admits of patterns of very large dimensions. This kind of engraving will be best understood by persons acquainted with figure-weaving; and especially with the manner of mounting the looms for that purpose. In that System, (see [Plate 50], [fig. 8]) the patterns are drawn on ruled paper divided into squares; and each of these squares represents a point in the texture, composed of one or more threads each way; insomuch that whenever that square has any desired colour in it on the pattern, it’s threads are taken by the person who prepares the loom; and they are missed in every case where nothing appears in that square, or a colour not then wanted. Now, whatever be the dimensions of these elementary points on the loom, they may be represented by squares of any convenient size on the pattern: only remembering that the smaller they are, in reality, the better will be the delineation. Thus in carpeting, for example, an element of this kind may be a square of one tenth of an inch and more; while one on a ribbon or a piece of silk, is often not the hundredth part. And therefore, the perfection of this engraving depends on the fineness of the points of which the figures are composed. For, in a word, this System proceeds on the same principle. When any part of a line requires a dot or mark to be made, the Machine strikes a blow there; and when no impression is to be made, the Machine (by means that will be shewn) suffers the cylinder to pass that place without striking. The means of regulating this is committed to workmen who merely know how to read off the pattern in it’s length, as it is now read off in it’s width by the weaver. To describe the construction of the Machine, (as exhibited in [figs. 3 and 4] of [Plate 50]) A is the cylinder to be engraved; and B is a worm-wheel fixed to it’s mandril, and destined to turn it. This it does, slowly, by the endless screw a, as turned by proper straps on the fast and loose pullies b c, ([figs. 3 and 4]). C shews a second wheel, concentric with that B, but running loose on it’s axis, which is a pin fitted into the end of the mandril. This wheel, when the threads of the screw a are fine, requires a motion more rapid than the wheel B—to give which motion by means of the latter, we use a pair of multiplying wheels d, which geer, one in the larger bevil wheel cut near the edge of the wheel B; and the other in a smaller bevil wheel cut or fixed on the inner face of the wheel C—and whence this latter wheel receives a velocity of about ten times the speed of B. The use of this wheel C, is to carry, across the Machine, certain bars, of wood or metal, shewn in [figs. 5 and 6], whose function is to carry short pins or studs 1, 2, 3, 4, &c. for the purpose of determining the places where the punch is to act, and where it is not. To this end, g h is a frame, which is raised by a cam or tappet i, fixed in the endless screw a, once every turn; and that through the medium of the little tumbler i e f, by which is finally determined whether the stroke shall take place or not—for m being a section of the stud bar of [figs. 5 and 6], it’s pins, when they occur, raise the end f of the bent lever f e i; and when there is no pin or stud in m, this lever is not raised, and the point i, does not come near enough to the cam to be laid hold of, in which case no stroke is given. This then, is so whenever the studs fail in the bar m; and these fail whenever the pattern-reader has said to the stud-setter, miss: and they occur whenever he has said take—both which cases happen more or less often according to the state of the squares in the pattern.