6i2 MECHANICAL EFFECTS OF THE DISCHARGE. 



the vessel, or if the charge be very strong, the disturb- 

 ance of the water may be so violent as to break the vessel. 



For the contrivance fig. 332 the wires are prepared first, the 

 straight ends being filed neatly round. The plate, which may, of 

 course, be of any shape, not necessarily square, is heated to the 

 melting point of sealing-wax, and a small ring of the wax is laid 

 on in the middle, with two branches extending in a straight line on 

 opposite sides of the ring. When the wax is cool the wires are 

 heated to the melting point of sealing-wax and placed in position 

 upon the lines of sealing-wax on the plate. When they are fixed 

 in the sealing-wax more of the wax is laid on the ring until it forms 

 a wall about 3 mm high. The distance of the points of the wires 

 must not exceed that mentioned previously, or no powerful dis- 

 charge will take place. 



For the glass vessel in fig. 333 one of the small drinking vessels 

 used for cage birds may be employed. The clamps are made of 

 brass wire which has not been softened in the flame ; the form into 

 which the wire is bent is seen from the figure. They should be 

 somewhat elastic, so as to ride firmly on the g]ass, and after they 

 are once adjusted care must be taken not to displace them again 

 when the vessel is placed on the little table of the discharger. Even 

 for strong charges the distance of the wires should be but small. 



The disturbance caused when the electric discharge 

 passes through air may be shown by a contrivance 

 which differs from that in fig. 330 only in this, that the 

 two wires are not connected by a strip of tinfoil, but 

 are bent so as to approach one another very closely at 

 the ends, 1 or 2 mm for small charges, a little more for 

 powerful ones. A weak discharge makes the drop of 

 water oscillate to and fro, a stronger one convulses the 

 air in the bottle so much that the drop is projected out 

 of the tube. 



With very strongly charged jars the apparatus in fig. 

 327 (often called the ' electric mortar ') may be employed 

 to exhibit the mechanical action of the discharge 

 upon air. A cork, a few millimetres wider than the 



