Beck-Chapman Opaque Illuminator. 
This illuminator was originally devised by Messrs. Chapman & Aldridge, and has been 
modified and sold under various trade names. A modification (patent applied for) is here introduced 
which simplifies the apparatus without injuring its utility. With the Beck aplanatic ring illuminator, 
the size of the object that can be examined is limited to about 3 in., whereas with the Beck-Chapman 
illuminator, the size of the object is immaterial. 
The construction of this apparatus is shown in Fig. 
6. The light from a small electric bulb (A) is thrown 
from the side into the microscope, through a condensing 
lens (B), upon a mirror (C) placed above the object glass 
(D). The mirror has an aperture in the centre. The mir- 
ror throws an annular ring of light, upon metal reflectors 
(E, E’ and E”’), which surround the object glass and 
concentrate the light upon the focal plane of the object 
glass giving a brilliant illumination upon any object or 
surface being examined. The light falls upon the object 
in the form of a hollow cone, so that no direct light enters 
the microscope and the object is rendered visible by 
s reflected light. 
To avoid the necessity of adjusting the height of 
an independant lamp when objects of a different thick- 
ness are being examined, a self-contained source of light 
is provided, consisting of a 6 volt lamp with condensing 
lens, in a well ventilated lamp-house, giving the necessary 
adjustments for the lamp. This lamp may be used with 
No. 2340. batteries or accumulators, or with suitable resistance or 
transformer from the mains. The mount of the illumin- 
ator, with its angular mirror, lamp-house and condenser, screws into the microscope by means of a 
revolving fitting (G). Its lower portion has a dovetailed slide (H) into which the various 
object glasses, with their reflectors are fitted. The illuminator is made with 14 in. (32 m/m.), 
Zin. (16 m/m.), 4 in. (8 m/m.) and } in. (4 m/m.) object glasses. The construction of the 
reflectors is varied according to the magnifying power of the object glass, so that either a larger 
or smaller field of view is illuminated. The illustration shows the two different forms. 
If a specially intense source of light is re— 
quired for photomicography, the 6 volt lamp 
can be withdrawn and light from our small arc 
lamp (No. 2685) or other powerful source can 
be directed into the aperture of the illuminator. 
This will only be necessary for special purposes, 
and is generally too powerful for visual observa- 
tion. 
Both this form of illuminator and the aplan- 
atic ring illuminator avoid any glare set up by 
reflections from the lenses of the object glass which 
are inevitable when so-called vertical illumination 
is used. The two methods are different in the 
results obtained. For polished metal specimens, Fig. 6 
vertical illumination is usually preferred, but for unpolished specimens the illumination given_by 
the Beck-Chapman or aplanatic ring illuminator is more satisfactory. 
No. 2340. Beck-Chapman illuminator, mount only, with lamp-house, illuminant, 
mirror and condenser, in case aoe 23: ae see ers hy peee LO 15 0 
Nor 2041-2 1510.(32 mijn) eObject glass swith reflectors 7.) era) see ee 
No. 2342. in. (16 m/m.) Object glass, with reflector ... ae es ae: ome elo RO 
No. 2343. 4in. (8m/m.) Object glass, with reflector ... a3 oe sei seh 610 0 
No. 2344. jin. (4m/m.) Object glass, with reflector ... at sf Ss eae 8 10: 0 
No. 2345. Green and ground glasses to fit ... ae an soe so per pair O25 86 
52 
