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Glass New Pocket Cyclopaedia
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New Pocket Cyclopædia, title page "New Pocket Cyclopædia: or, Elements of Useful Knowledge, Methodically Arranged, with Lists of Select Books On every important Subject of Learning and Science; designed for the Higher Classes in Schools, and for Young Persons in General. By John Millard, Assistant-Librarian of the Surry Institution. Second Edition, with many important additions and corrections. London: Printed for Sherwood, Neely, and Jones, Paternoster Row. 1813." New Pocket Cyclopædia, page 602
See the scan at google books.

...page 602...

A very great improvement in ship-building has been made, within a few years, by introducing Glass Illuminators, or lenses into the decks and port-holes of ships, which convey light so as to enable the men to work, or do any repairs, in tempestuous weather, when the hatches are closed. A patent for these illuminators has been granted to PELLATT and GREEN of St. Paul's Church-yard.
The illuminator is a piece of solid glass, of a circular or elliptical form at the base; but the circular form is the most productive of light, and the strongest against accident: it is convex on the side to be presented outwards, to receive and condense the rays of light, and has a flat or plane surface on the inside of the room or apartment which it is intended to light. It is, or approaches to a segment of a sphere, or spheroid; it is, in fact a lens; both sides may, in general, be left polished; but when the illuminator is to be placed in a situation where any danger may be apprehended of its being acted upon as a burning glass, one side, at least, should be ground or roughed. Its size is various according to the purpose, or situation, for which it is designed, and its convexity is increased or diminished, according to the size required. The ordinary dimensions are a base, of about five inches in diameter, to one half-inch in height, from the centre of the base; the illuminator is fixed in a square or circular frame, made of wood or of metal, with glaziers' putty, or other cement.¹

¹The patent illuminators have been introduced, with complete success, into private dwellings, instead of sky-lights; and particularly, in the ceilings of cellars and under-ground offices. Carriages have passed over these illuminators daily, without breaking them, or producing any bad effect.