Bauhaus-Universität Weimar

Titel:
Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Person:
Wright, Lewis
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39439/333/
LANTERN POLARISING APPARATUS 
347 
re-reflected into a horizontal direction and polarised by 
the pile p with a black glass at the bottom. This arrange¬ 
ment can be made cheaply and readily of any size desired. 
It will be observed, that while the horizontal direction of 
the beam from the lantern is preserved in the Delezenne 
polarisers, it is necessarily deflected several inches to one 
side of the axis of the flange-nozzle. In the first instruments 
made on this principle, the beam was brought down below 
the nozzle ; but this makes the apparatus rather deep, and 
requires a deep case for packing. To avoid this the polariser 
Fig. 194.—Direct Reflecting Polariseope 
was turned sideways ; but that was found awkward, and also 
necessitated a large case. To meet these objections I advised 
reversing the polariser so as to deflect the beam upwards, and 
Messrs. Newton & Co. now construct their instruments as 
in fig. 194. It will be seen that it is then rendered quite 
compact, and requires no larger a case than the Nicol prism 
polariseope. All the front portion is precisely the same as in 
the instrument shown in section in fig. 190. 
Such polarisers are liable to the same objection as the 
elbow form, not being capable of rotating the polarised beam. 
This can, however, be effected through a simple expedient 
suggested by Professor S. P. Thompson. If we cause the po¬ 
larised rays to pass through a mica quarter-wave plate (§ 211)
        

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