174 THE ART OF PROJECTING. 



with an oval hole three inches in its longer and two 

 inches in its shorter diameter. One with two holes one 

 inch in diameter and an inch and a half 

 apart, the two holes horizontal. Oue 

 with two holes like the last except that 

 one is to be over the other. One with three holes each 

 an inch in diameter, their centres two and a half inches 

 apart. One with a hole two inches square. Two 

 saucers or other crockery vessels presenting as large 

 a fluid surface when filled as convenient, may be filled, 

 one with the strongest ammonia water, the other with the 

 strongest hydrochloric acid, and placed in the box 

 and the back closed. The box will at once be filled with 

 the dense white vapor of ammonium chloride. If the 

 solutions be heated before being placed in the box the 

 fumes will be denser still, and therefore better for this 

 purpose. 



EXPERIMENTS. 



1. Strike the cloth back of the box with the hand 

 suddenly. A white ring five or six inches in diameter 

 will be projected and will move several feet. If the 

 smaller three inch hole be in front, the ring will be 

 smaller and will move faster. 



2. Produce a ring by swinging the back of the box 

 an inch or two and letting it strike the box smartly. 

 The ring will move with rapidity fifteen or twenty feet 

 in the air, going in a straight line if there be no 

 currents of air to deflect it or objects near to its path. 



3. If the table be ten feet long or more and the box 

 be at one end of it, so that the rings may move over the 

 length of the table, a swift moving ring will come 

 down to it and be broken, as if the table attracted it. 

 To prevent this, tilt up the box, being careful about 



