Crown glass Sentence Examples

These differences arise primarily from the fact that glass for optical uses is required in comparatively large and thick pieces, while for most other purposes glass is used in the form of comparatively thin sheets; when, therefore, as a consequence 5 and crown glass.

Crown-glass has at the present day almost disappeared from the market, and it has been superseded by sheet-glass, the more modern processes described above being capable of producing much larger sheets of glass, free from the knob or " bullion " which may still be seen in old crown-glass windows.

For a few isolated purposes, however, it is desirable to use a glass which has not been touched upon either surface and thus preserves the lustre of its " fire polish " undiminished; this can be attained in crown-glass but not in sheet, since one side of the latter is always more or less marked by the rubber used in the process of flattening.

One of the few uses of crown-glass of this kind is the glass slides upon which microscopic specimens are mounted, as well as the thin glass slips with which such preparations are covered.

A full account of the process of blowing crown-glass will be found in all older books and articles on the subject, so that it need only be mentioned here that the glass, instead of being blown into a cylinder, is blown into a flattened sphere, which is caused to burst at the point opposite the pipe and is then, by the rapid spinning of the glass in front of a very hot furnace-opening, caused to expand into a flat disk of large diameter.

In 1302 window glass, probably crown-glass, was made at Beza le Foret in the department of the Eure.

They are made usually of crown glass or rock crystal ("pebbles"), the latter being somewhat lighter and cooler to wear.

By studying the dispersion of colours in water, turpentine and crown glass Newton was led to suppose that dispersion is proportional to refraction.

Rutherfurd devised one made of flint glass with two crown glass compensating prisms; whilst Thallon employed a hollow prism containing carbon bisulphide also compensated by flint glass prisms. In direct vision spectroscopes the refracting prisms and slit are in the observing telescope.

The triple object-glass, consisting of a combination of two convex lenses of crown glass with a concave flint lens between them, was introduced in 1765 by Peter, son of John Dollond, and many excellent telescopes of this kind were made by him.

The primary reason for this retention is that nothing approaching the difference in dispersive power between ordinary crown glass and ordinary dense flint glass (a difference of i to 13) has yet been obtained between any pair of the newer glasses.

It consists of a piano-convex field-lens of crown glass.

If a collective system be corrected for the axis point for a definite wave-length, then, on account of the greater dispersion in the negative components - the flint glasses; - over-correction will arise for the shorter wavelengths (this being the error of the negative components), and under-correction for the longer wave-lengths (the error of crown glass lenses preponderating in the red).

The second aberration which must be removed from microscope objectives are the chromatic. To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration).

Their mineral crown glass lenses are precision ground, scratch resistant and allow natural light to pass through while providing maximum UV protection.

The crown glass used for eyeglass lenses has an index of refraction of 1.52.