If you place a piece of heavy paper or cardboard between two sharp wires connected to the secondary of a spark-coil and start the coil working, the paper will be pierced. A Practical Joke This action of the coil may be made the basis of an amusing joke. Offer a friend who may smoke cigarettes some cigarette paper which has been prepared in the following way. [Illustration: Fig. 169.—The Bulb will emit a Peculiar Greenish Light.] Place several sheets of the paper on a piece of sheet-metal which is connected to one side of the secondary. By means of an insulated handle so that you will not get a shock, move the other wire all over the surface of the cigarette paper. The paper will be pierced with numerous fine holes which are so fine that they can hardly be seen. If your friend uses any of the paper in making a cigarette and tries to light it he will waste a box of matches without being able to get one good puff, because the little invisible holes in the paper will spoil the draft. Perhaps he may quit smoking altogether. An Electric Garbage-can [Illustration: Fig. 170.—An Electrified Garbage-can.] If there are any dogs in your neighborhood that have a habit of extracting things from your ash-barrel or garbage-can, place the latter on a piece of dry wood. Lead a well insulated wire from one secondary terminal of your coil to the can. Ground the other secondary terminal. If you see a dog with his nose in the can press your key and start the coil working. It will not hurt the dog, but he will get the surprise of his life. He will go for home as fast as he can travel and will not touch that particular can again, even if it should contain some of the choicest canine delicacies. Photographing an Electric Discharge The following experiment must be conducted in a dark room with the aid of a ruby photographic lamp, as otherwise the plates used would become lightstruck and spoiled. [Illustration: Fig. 171.—Jacob’s Ladder.] Placed an ordinary photographic plate on a piece of sheet-metal with the coated side of the plate upwards. Connect one of the secondary terminals of the spark-coil to the piece of sheet-metal. Then sift a thin film of dry starch powder, sulphur, or talcum through a piece of fine gauze on the plate. Lead a sharp-pointed wire from the other secondary terminal of the coil to the center of the plate and then push the key just long enough to make one spark. Wipe the powder off the plate and develop it in the usual manner of films and plates. If you cannot do developing yourself, place the plate back in its box and send it to some friend, or to a photographer. The result will be a negative showing a peculiar electric discharge, somewhat like sea-moss in appearance. No two such photographs will be alike and the greatest variety of new designs, etc., imaginable may be produced in this manner. Jacob’s Ladder