** How to Make a Lead Pencil Rheostat [145]

Take an ordinary lead pencil and cut seven notches at equal intervals on the pencil down to and around the lead, leaving it bare.  A seven-point switch is constructed on a board of suitable size making the points by using screws that will go through the board.  A small piece of tin or brass will do for a switch and is fastened as shown.  The connections are made on the back side of the board as shown by the dotted lines.  This will reduce 40 to 50 volts down to 5 or 10 volts for short lengths

[Illustration:  Simple Rheostat]

of time.  —­Contributed by Roy Newby, San Jose, Cal.

** Homemade Shoe Rack [146]

The accompanying sketch explains how a boy can make his own shoe rack that can be placed on the wall in

[Illustration:  Shoe Rack]

the clothes closet.  Figure 1 shows the construction of the bottom to permit the dirt to fall through.  Two boards, 9 in. wide and about 3 ft. long, with six partitions between, as shown, will make pockets about 6 in. long.  The width of the pockets at the bottom is 2 in. and at the top 5 in.  —­Contributed by Guy H. Harvey, Mill Valley, Cal.

** How to Waterproof Canvas [146]

The method used by the British navy yards for waterproofing and painting canvas so it will not become stiff and cracked is as follows:  One ounce of yellow soap and 1/2 pt. of hot water are mixed with every 7 lb. of paint to be used.  The mixture is applied to the canvas with a brush.  This is allowed to dry for two days and then a coat of the same paint, without the soap, is laid on.  When this last coat is dry the canvas may be painted any color desired.  After three days of drying the canvas may be folded up without sticking together, and is, of course, waterproof.  Canvas waterproofed in this manner makes an excellent covering for portable canoes and canvas boats.  The color mixture for the soap and second application is made from 1 lb. of lampblack and 6 lb. of yellow ocher, both in oil; the finish coat may be any color desired.  When no paint is to be used on the canvas it may be waterproofed with a mixture made from soft soap dissolved in hot water, and a solution of iron sulphate added.  Iron sulphate, or ferrous sulphate, is the green vitriol.  The vitriol combines with the potash of the soap, and the iron oxide is precipitated with the fatty acid as insoluble iron soap.  This precipitate is then washed, dried and mixed with linseed oil.

** Building a House in a Tree Top [146]

The accompanying photograph shows a small house built in a tree top 20 ft. from the ground.  The house is

[Illustration:  Lofty Sentry Box for Guarding Watermelon Patch]

5 ft. wide, 5 ft. 1 in. long, and 6 ft. 6 in. high.  A small platform, 2 ft. wide, is built on the front.  Three windows are provided, one for each side, and a door in front.  The entrance is made through a trap door in the floor of the house.  This house was constructed by a boy 14 years old and made for the purpose of watching over a melon patch.  —­Contributed by Mack Wilson, Columbus, O.