Photo-micrographic apparatus No. 105 with small stand No. 106.
Large Projection Apparatus.
In this projection apparatus an electric projection lamp is made use of, the lamp being available for electric currents of 20 Ampères and about 48 Volts. To regulate the current a rheostat is necessary. When using constant current the carbons should stand at an angle in order to utilize to best advantage the stronger light of the positive (upper) carbon. For spectroscopic projections the carbons of the lamp have to be in vertical position.
Connected with the lamp is a triple condenser of 150 mm aperture. The latter should be protected from the heat-rays by a large mica-plate which is furnished with the apparatus.
Various devices permit very accurate adjustment of the lamp and condenser. For example, two thumb-screws control the position of the carbons of the lamp so that the luminous point may be readily brought into the exact optical axis of the condenser. Again, the two inner lenses of the condenser are moveable and are controlled by two knobs conveniently situated as shown in the illustration.
By this adjustment of the lenses of the condenser it is possible to do away with disturbing chromatic aberration. The rays of light leave the condenser in moderate convergence.
For direct projection from the preparation the apparatus consists of the optical bench upon which are mounted the various accessories in proper succession (Fig. p. [88]):
1. A large cooling cell, which is to be filled with water or alum solution.
2. The bellows with tube. This is connected with the cooling cell by means of a metal ring which slips over the end of the cell and is held in place by a screw. The metal ring is attached to one end of the bellows, while the other end carries a large tube.