Each post must be well braced to keep it rigid while a person is swinging on the bar.  Four anchors are placed in the ground at the corners of an imaginary rectangle 9 by 16 ft., in the center of which the posts stand as shown in Fig. 2.  Each anchor is made of one 2-ft. piece of wood, around the center of which four strands of the heavy galvanized wire are twisted, then buried to a depth of 2 ft., the extending ends of the wires coming up to the surface at an angle.

The heavy screw eyes are turned into the posts at the top and lengths of ropes tied to each.  These ropes or guys pass through the pulley blocks, which are fastened to the projecting ends of the anchor wire, and return to the posts where they are tied to cleats.  Do not tighten the guy ropes without the bar in place, as to do so will strain the posts in the ground.  Do not change the elevation of the bar without slacking up on the ropes.  It takes but little pull on the guy ropes to make them taut, and once tightened the bar will be rigid.

[Illustration:  Ground Plan]

Oil the bar when it is finished and remove it during the winter.  It is well to oil the wood occasionally during the summer and reverse the bar at times to prevent its becoming curved.  The wood parts should be well painted to protect them from the weather.

** Electrostatic Illumination [299]

Anyone having the use of a static machine can perform the following experiment which gives a striking result.  A common tumbler is mounted on a revolving

[Illustration:  Illuminated Tumbler]

platform and a narrow strip of tinfoil is fastened with shellac varnish to the surface of the glass as follows:  Starting beneath the foot of the glass from a point immediately below the stem, it is taken to the edge of the foot; it follows the edge for about 1 in. and then passes in a curve across the base, and ascends the stem; then it passes around the bowl in a sinuous course to the rim, which it follows for about one-third of its circumference; after which it descends on the inside and terminates at the bottom.  The tinfoil on the outside of the glass is divided by cutting with a knife every 1/8 in., the parts inside and beneath the glass being left undivided.  Current is then led from a static machine to two terminals, one terminal being connected to one end of the tinfoil strip, and similarly the second terminal makes contact with the other end.  As soon as the current is led into the apparatus, a spark is seen at each place where the knife has cut through the tinfoil.  If the tumbler is rotated, the effect will be as shown in the illustration.  A variety of small and peculiar effects can be obtained by making some of the gaps in the tinfoil larger than others, in which case larger sparks would be produced at these points.  The experiment should be carried out in a darkened room, and under these circumstances when nothing is visible, not even the tumbler, the effect is very striking.