** Cost of Water [435]

The average cost of supplying 1,000,000 gal. of water, based on the report of twenty-two cities, is $92.  This sum includes operating expenses and interest on bonds.

** How to Make a Wondergraph [436] By F. E. Tuck

An exceedingly interesting machine is the so-called wondergraph.  It is easy and cheap to make and will furnish both entertainment and instruction for young and old.  It is a drawing machine, and the variety of designs it will produce, all symmetrical and ornamental and some wonderfully complicated, is almost without limit.  Fig. 1 represents diagrammatically the machine shown in the sketch.  This is the easiest to make and gives fully as great a variety of results as any other.

To a piece of wide board or a discarded box bottom, three grooved circular disks are fastened with screws so as to revolve freely about the centers.  They may be sawed from pieces of thin board or, better still, three of the plaques so generally used in burnt-. wood work may be bought for about 15 cents.  Use the largest one for the revolving table T. G is the guide wheel and D the driver with attached handle.  Secure a piece of a 36-in. ruler, which can be obtained from any furniture dealer, and nail a small block, about 1 in. thick, to one end and drill a hole through both the ruler and the block, and pivot them by means of a wooden peg to the face of the guide wheel.  A fountain pen, or pencil, is placed at P and held securely by rubber bands in

[Illustration:  An Easily Made Wondergraph]

a grooved block attached to the ruler.  A strip of wood, MN, is fastened to one end of the board.  This strip is made just high enough to keep the ruler parallel with the face of the table, and a row of small nails are driven part way into its upper edge.  Anyone of these nails may be used to hold the other end of the ruler in position, as shown in the sketch.  If the wheels are not true, a belt tightener, B, may be attached and held against the belt by a spring or rubber band.

After the apparatus is adjusted so it will run smoothly, fasten a piece of drawing paper to the table with a couple of thumb tacks, adjust the pen so that it rests lightly on the paper and turn the drive wheel.  The results will be surprising and delightful.  The accompanying designs were made with a very crude combination of pulleys and belts, such as described.

The machine should have a speed that will cause the pen to move over the paper at the same rate as in ordinary writing.  The ink should flow freely from the pen as it passes over the paper.  A very fine pen may be necessary to prevent the lines from running together.

The dimensions of the wondergraph may vary.  The larger designs in the illustration were made on a table, 8 in. in diameter, which was driven by a guide wheel, 6 in. in diameter.  The size of the driver has no effect on the form or dimensions of the design, but a change in almost any other part of the machine has a marked effect on the results obtained.  If the penholder is made so that it may be fastened at various positions along the ruler, and the guide wheel has holes drilled through it at different distances from the center