. The microscope; a simple handbook. Microscopes. 42 THE MICROSCOPE Colour screens. than the Beck illuminator, but most prefer the thin glass form for high powers, and the Sorby reflector for low-power work. As a convenient and universal illuminator for all powers where the highest resolution is not required, the prism illuminator, especially with an electric light bulb attached to it, is popular for metallurgical work. Fig. Ill (p. 120) shows this illuminator provided with a small focussing lens, a receptacle for colour filters, and a 16-candle-power electric light to suit either the 100- or
. The microscope; a simple handbook. Microscopes. 42 THE MICROSCOPE Colour screens. than the Beck illuminator, but most prefer the thin glass form for high powers, and the Sorby reflector for low-power work. As a convenient and universal illuminator for all powers where the highest resolution is not required, the prism illuminator, especially with an electric light bulb attached to it, is popular for metallurgical work. Fig. Ill (p. 120) shows this illuminator provided with a small focussing lens, a receptacle for colour filters, and a 16-candle-power electric light to suit either the 100- or 200-volt current in a metal casing. Colour screens are of use for several important purposes. They are either coloured glasses or coloured gelatine mounted between two glasses. They give greater contrast where objects being examined are stained or are naturally coloured, and give truer rendering of natural colours where artificial light is em- ployed. Every substage con- denser should be sup- plied with a green glass, but a set of difierent coloured screens is very useful for increas- ing colour contrasts, both for visual and photomicrographic work. If a specimen of bacteria is stained faintly with red, the use of a green screen will make them appear almost black and much more distinct. If a specimen is stained— Blue, a red filter should be used. Green, a red „ Red, a green „ Yellow, a blue „ Brown, a blue „ Purple, a green „ Violet, a yellow „ If the screen is too dark, and the light and shade contrast too great in consequence, fine detail in the structure may be somewhat clogged or obscured, but faintly stained or coloured specimens are rendered much more visible by the use of the correct colour filter. Another marked advantage in the use of colour filters of green or blue is obtained by the greater power they give to an object glass of resolving fine Please note that these images are extracted from scanned page images that may have been digitally en
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