634 HEATING EFFECTS OF THE DISCHARGE. 



be slightly curved, not pointed. The ends of the strip are attached 

 to the wires by pasting round strip and wire another strip of tin- 

 foil, 5 mm wide and 10 mm long. 



While by means of a single jar the heating effect of the discharge 

 can only be jnst rendered visible, a powerful discharge is capable of 

 fusing, and even igniting, the strip of tinfoil. For this purpose 

 several jars must be joined together ; they then form a so-called 

 electric lattery. It usually consists of four or more jars, pretty 

 large and of nearly the same size, whose internal and external coat- 

 ings are respectively connected with each other. The external 

 coatings are usually connected by placing the jars upon a common 

 conducting surface, for example, a sheet of cardboard or a wooden 

 board covered with tinfoil, or by placing them in a shallow wooden 

 box lined with tinfoil. The internal coatings are connected together 

 either by metallic rods, which are inserted into holes made for the 

 purpose in the knobs of the jars, or more simply by passing a 

 moderately stretched metallic chain round the metal rods of the jars ; 

 the end of the chain may be used at the same time for connecting 

 the battery with the conductor of the machine. 



For many experiments with the electric battery a so-called 

 universal discharger (Henley's) is almost indispensable. It consists 

 of a wooden stand which carries two short insulating pillars, each 

 provided with a joint in which moveable metal rods are fitted. 

 Between these pillars is a small table on which the object under ex- 

 periment is placed. A simple apparatus of this kind may be con- 

 structed by fixing upon a small wooden board, 8 cm from one another, 

 in a line, three very stout sticks of sealing-wax, the middle one 

 being 7 cm and the two outer ones 10 cm high. The middle stick 

 carries a thin round board, 6 cm in diameter, cut out of a cigar-box ; 

 to the tops of the two outer sticks corks are fixed horizontally. Two 

 pieces of brass wire, from 15 to 18 cm long and 2 mm thick, are 

 softened from end to end in the flame, one end of each is bent into 

 a ring, and the straight part is pushed horizontally through one of 

 the corks, which are perforated for the purpose with the bradawl. 

 By moving the wires nearer and farther from one another, and 

 bending them suitably, their ends may be placed in any position re- 

 quired for each experiment. 



In order to fuse a strip of tinfoil the straight ends of the wires 

 are turned towards each other and kept 6 cm apart. A small strip 

 of tinfoil is fastened between them in the manner explained pre- 

 viously, and one of the rings of the universal discharger being con- 

 nected by a chain with the tinfoil support of the battery, a small 

 chain is attached by one end to the other ring, and by the other 



