Page:The American Boy's Handy Book edition 1.djvu/402

between his lips, he filled his cheeks, and blew the smoke into the paper box. By this time all the idlers in the office had Image missingHow to make a Card-box. collected around the smoker, who, with a triumphant smile upon his face, commenced to tap the sides of the box with his lead-pencil. At each tap a tiny but perfect and beautiful ring of smoke shot into the air—one hundred and ten were counted before the smoke was exhausted. Fig. 236 shows how similar rings can be made with a lamp-chimney in which a card disk with a hole in it has been placed; a piece of paper or membrane fastened over the other end serves for a vibrating surface, which, when struck with the thumb, forces out the little rings of smoke.

The reader must not for a moment suppose that it is necessary to use tobacco smoke to perform this beautiful experiment; any other smoke will answer just as well to make the "vortex rings," as they are scientifically called. If after dipping a paint-brush into india ink, or any water-color paint, you gently insert the tip of the brush into a glass of clear water, you will see the pigment fall from the end of the brush, and, gradually sinking to the bottom, form rings exactly similar to the circles of smoke described.

The rings made by skipping a flat stone over the water are but another example of the vortex, and the jolly commercial traveller, when he was exhibiting the little paper box and