Bauhaus-Universität Weimar

The Art of Projecting. A Manual of Experimentation in Physics, Chemistry, and Natural History with the Porte Lumière and Magic Lantern
Dolbear, A. E.
second plain mirror at r, which should have such an 
inclination as to reflect the converging rays upon the 
object to be shown at d, and strongly illuminate it ; the 
objective at o will be used in the same way as for any 
other projection. This apparatus should be in a box 
made with sides a foot square and six or eight inches 
deep. At the back of it a hole should be left at d9 in 
which the various objects for exhibition may be held. 
* In place of the condenser and the plain mirror, a 
large concave reflector, such as is used behind lamps, 
may be placed at r9 and the parallel rays from the porte 
lumière allowed to fall upon it. It should be placed at 
such a distance from the object d9 that it will just illu¬ 
minate it; this will of course be determined by the 
focal length of the mirror. 
The room needs to be quite dark for the successful 
working of this apparatus, and especial care should be 
taken to prevent any of the light from the porte lumière 
from being scattered into the room ; paint the box black, 
inside and out, with lampblack mixed in japan varnish. 
If the lime light be used, as it generally is for such 
an exhibition, it is necessary to modify the lantern very 
much,—so much so as to require an entirely new in¬ 
strument. The following is the simplest plan of one : 
A Square wooden box made eighteen or twenty inches 
on a side, and about fifteen inches deep, may have a 
little way made in it on one side for the fixtures holding 
the jet i and the lime j to slide upon. A hole r cut 
six inches square, may be made near the corner, and 
another one on the front side for the light to come 
through upon the lens of which is the only lens needed 
for work. The size of this hole should be no greater 
than that of the lens o used for the projections, but this 
lens should be as large as possible. A lens six or eight


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