Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
automatic lamp where the arc has to be ‘ struck ’ or formed at 
starting by touching the carbons together by a hand movement, 
and then separating them, the lamp then remains burning, the 
carbons as they consume away being pushed up by springs against 
steel screws, somewhat after the manner of the ordinary carriage 
candle lamps, and this lamp also performs well where the current 
is steady and not too high in voltage ; but in practice I myself prefer 
hand-fed lamps to any on account of their simplicity and freedom 
from any liability to fail or become unsteady at a critical moment. 
Of large automatic arc lamps little need be said ; those described 
in Chapter XII. remain as the general pattern still in use. Messrs. 
Oliver have brought one out on the same lines as the Brockie Pell 
therein described, which is extremely steady and reliable, and is 
in my opinion the best of such lamps at present on the market. 
Messrs. Newton also make large hand-fed lamps for their 
triple rotating and similar lanterns, and these are by some operators 
preferred to even the ‘ Oliver ’ lamp. 
Projection microscope.—Various slight improvements, both 
optical and mechanical, have been made in this instrument since 
1890. Of these the most important has been the introduction of a 
quadruple condenser, with a view to still further reducing spherical 
aberration in the lantern portion of the instrument. After many 
years of experiment, the new condenser, as designed by my father, 
reduces this fault to a minimum, and a considerable gain in both 
light and definition is the result. With the new arrangement 
apochromatic lenses especially show to more advantage than formerly. 
Of lenses, several new ones have been brought out which perform 
well with the projection microscope. Herr Reichert has intro¬ 
duced an oil-immersion lens, nominally \ but really 1 focus, of 
N A 1*80 to 1’32, which for moderately high power is as good an 
all-round projection-lens as I know of. As this lens lias a very great 
working distance, it is as well to ask for a shortening of this if 
required chiefly for projection, as the horizontal position tends to 
drain the oil away. 
The Zeiss apochromatic § of N a R40 does magnificent work, 
but is very costly. 
I can also speak from experience of Messrs. Swift’s Vj oil 
immersion at 51. 5s. ; this also for all-round work can hardly be 
beaten, and Messrs. Leitz also do a fine series at a moderate price. 
Of mechanical improvements the most important has been the


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