Step One: Punch a quarter-inch hole in the cardboard. Cut and glue a piece of foil on the card to cover the hole. Do not get any glue over the hole. Gently poke the needle through the foil. Make the pinhole round and smooth; the more round the hole, the better your microscope will work.
Step Two: With the tip of a toothpick, carefully pread a thin layer of petroleum jelly just around the hole on both sides of the foil. Make sure to keep the hole open, free of jelly. With an eyedropper, squeeze a drop of clean distilled water into the pinhole. The petroleum jelly should hold the water in the pinhole. You may have to tap the card gently to get the water
in the hole.
Step Three: Point the flashlight upward. Place the object you want to study over the light. Look at the object through the water drop.