A New Approach to Overhead Projection Timothy L. Schaap 311 Jon Court, Des Plaines, IL 60016 Recently I h a d the pleasure of attending a seminar in L a Salle, Illinois. resented bv H u h e r t Alvea. the master of the overhead projkctor (among other thingsj.1 T h i s rekindled memories of yearly visits which Alyeahad made t o N o r t h e r n Illinois University in m y undergraduate days. I was reminded how impressive it is t o see a n experiment proiected t o fill comple~elyan 8 ft X 8 ft screen. Ifeel t h a t the only obstacle t o the widespread use o f this technique has been t h e need t o construct a special projector, so I would like t o suggest a simple
modification t h a t can be made t o a n ordinary o v erhead ~ proiector. Turn the overhead projector onto i t s back2 a n d affix a n ordinary m i r r o r t o the projector as shown in the figure. Use a clamp and ringstand t o hold the mirror in place. B y holding or otherwise securing a n Alyea cell or ordinary test tube hetween the l i g h t source and the mirror, one can carry o u t demonstrations t h a t can be seen by everyone in the room.3
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Aiyea's feature column "TOPS" (Tested Overhead Projection from January 1962 through January 1971 Series) ran in THIS JOURNAL and is also available in a reprint volume from subscription and Book Order Department, JOURNALOF CnEMiCAL EDUCATION,20th and Northampton Streets, Easton, PA 18042 for $8.35 ($9.25 foreign) prepaid. Readers are referred to ewer of these sources for a wide range of demonstrations adapted to the overhead projector. Teachers should be aware, however, that some brands of overhead projectors may have safety switches which automatically turn off the projector if it is tipped over. Also, when placing the projector on its side. be sure not to cover up the ventilation slots which are used for coolino. Unless the proiector mage is very nlgh up on the screen. tne pro,ector flse f may block the Ibght from the lower [hard of the mage Thls prob em can oe overcome by propp ng up the edge of the prqector nearest the mirror on a block.
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Schematic of ihe projection apparatus. The mirror is adjusted to reflect from the projection head.
Volume 6 1
Number 2
February 1984
145
