a contrivance for blowing the fire, for the fusion of ores, without bellows; by means of water falling through a funnel into a clofe vessel, which sends from it so much air or vapour as continually blows the fire: if there be the space of another vessel for it to expatiate in by the way, it there lets fall its humidity, which otherwise might hinder the work. This contrivance was named camera AEOLIA by Kircher.

CAMERA Lucida, a contrivance of Dr Hook for making the image of any thing appear on a wall in a light room, either by day or night. Opposite to the place or wall where the appearance is to be, make a hole of at least a foot in diameter, or if there be a high window with a casement of this dimension in it, this will do much better without such hole or casement opened. At a convenient distance, to prevent its being perceived by the company in the room, place the object or picture intended to be represented, but in an inverted situation. If the picture be transparent, reflect the sun's rays by means of a looking-glass, so that they may pass through it towards the place of representation; and to prevent any rays from passing aside it, let the picture be encompassed with some board or cloth. If the object be a statue, or a living creature, it must be much enlightened by calling the sun's rays on it, either by reflection, refraction, or both. Between this object and the place of representation put a broad convex glass, ground to such a convexity as that it may represent the object distinctly in such place. The nearer this is situated to the object, the more will the image be magnified on the wall, and the further the lens; such diversity depending on the difference of the spheres of the glasses. If the object cannot be conveniently inverted, there must be two large glasses of proper spheres, situated at suitable distances, easily found by trial, to make the representations erect. This whole apparatus of object, glasses, &c. with the persons employed in the management of them, are to be placed without the window or hole, so that they may not be perceived by the spectators in the room, and the operation itself will be easily performed. Phil. Trans. No. 38. p. 741, seq.

CAMERA Obscura, or Dark Chamber, in Optics, a machine, or apparatus, representing an artificial eye; whereon the images of external objects, received thro' a double convex glass, are exhibited distinctly, and in their native colours, on a white matter placed within the machine, in the focus of the glass.

The first invention of this instrument is ascribed to Baptista Porta. See his Magia Naturalis, lib. xvii. cap. 6. first published at Frankfort about the year 1589 or 1591; the first four books of this work were published at Antwerp in 1560.

The camera obscura affords very diverting spectacles; both by exhibiting images perfectly like their objects, and each clothed in their native colours; and by expressing, at the same time, all their motions; which latter no other art can imitate. By means of this instrument, a person unacquainted with designing will be able to delineate objects with the greatest accuracy and justness, and another well versed in painting will find many things herein to perfect his art. See the construction under DIOPTRICS.