Of flint glass must be chosen; the latter, although the weaker, corrects the other chromatically by its greater dispersive power.
In its modern form the Leyden jar consists of a widemouthed bottle of thin English flint glass of uniform thickness p. 512.
Lines, such as C and F, yet the flint glass prism will show a relative drawing out of the blue end and a crowding together of the red end of the spectrum, while the crown prism shows an opposite tendency.
The prisms are necessarily compound, and usually consist of flint glass with compensating prisms of crown.
The prism may be made of a dense flint glass or of quartz if the ultra-violet is to be explored, or it may be hollow and filled with carbon bisulphide, a-bromnaphthalene or other suitable liquid.
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.
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 front lens is made of baryta light flint glass 3.