1815. A new Concept VisuaI Teaching Aids:

The Overhead or writing projector is a simple instrument for making the lecture and teaching more effective. Transparencies upto 25x25 cms can be projected from its horizontal, flat stage, on the wall or screen at a very short distance behind the lecturer Serves both as a black board and projector combined.
The lecturer can now conntinuously face his audience. draw the pictures or write as he talks, or even use ready made multicoloured transpare ncies to make his lecture more dynamic. The lecturer writes with ordinary grease /coloured pencils or fibre point pens on the transparent stage, and the "WRITTEN" is sinultaneously projected on the wall behind.

Applications

Diagramme / lIIustrtions Datums, Tables Etc. : Drawn or printed in multicolours and transparent material can be instantly projected on the rear wall, and preserved notes can be instantly emphasised.

Working Models: Made of different coloured transparent and opaque materials can also be projected so as to demonstrate complex mechanisms and their actual working, like internal combustion engine, train of gears, lock mechanism, Air craft parts etc.

Dynamic Demonstrations: Such as formation of magnetic field by using iron fillings on a transparent sheet and a magnet. crystal formation, or ripple tank demonstations in shallow plain glass tray or Experiments on CONVECTION CIRCULATION, chemicaI changes by heat and the effects of electric currents electolysiscan also be demonstrated.

Structural Approach: By super-imposing 2-3 or even more colour transparencies step by step, and also check asimilation of the audience by quiz testing etc.

Technical Specifications Body: All steel thick guage weided construction stove enamelled. Over all dimensions 35x55x75 cms.

Opticals : A special wide Angle PERISCOPIC CONVEX projector lens of 90 mm. dia and 28.5x28.5 original Fresnels double condenser.

Elevation Device: A surface ALUMINIZED and SILICON COATED, glass reflector is tiltable through a convenient knob positioned on the head elevating the screen image 5° to 30°.

Focussing: By two large rotary knobs. via self Iocking cogwheel toothed racks. Adjustment is infinitely variable and absolutely, smooth.

Illumination: Through a 1000 watt. medium prefocus, T-20 screw base projection lamp positioned at the optical axis of a highly silvered concave reflector.

Cooling System: An efficient high speed motorised cooling fan. working noiselessly on exhaust.

Operating Switches: Two special toggle switches, with symbols for the Fan and lamb.
Safety Measures: For protection of lamp and fresnels lens etc. a Thermostat in Circuit starts the fan Automatically within 25 Seconds of switching on the lamp, andturns off, of its own only after the lamp is sufficiently cooled.

Writing Scroll: A roll up scroll of transparent sheet10"x8 meters, built-in a metallic frame is attachable to the projector stage by 4 knurled Knobs.