The diaphragm, B, which is the essential part of the instrument, should be made as carefully as possible from ferrotype tin, commonly called tintype tin.  Cut a circular piece from this metal the exact size of the outside of the shell.  A hole is made in the center of the disk a little larger than a binding-post that is taken from another old battery cell.  When making the hole in the disk be careful not to bend or crease the tin.  Scrape the black coating from the tin around the outside about 1/4 in. wide and a place about 1 in. in diameter at the center.

The second electrode, C, is made the same as D, and fastened to the tin diaphragm with the binding post without using any insulation.  A third binding post, G, is fastened to the shell through a drilled hole to make the other terminal.  The mouthpiece, A, may be turned from wood in any shape desired, but have a flange on the back side that will make a tight fit with the outside of the shell.

Fill the paper tube with powdered carbon, E, which can be made by pounding and breaking up pieces of carbon to about the size of pin heads.  Powdered carbon can be purchased, but if you make it be sure to sift out all the very fine particles.  Assemble the parts as shown and the transmitter is ready for use.  If speech is not heard distinctly, put in a little more, or remove some of the carbon and try it out until you get the instrument working nicely.  —­Contributed by Harold H. Cutter, Springfield, Mass.

** Quickly Made Lawn Tent [398]

A very simple way of erecting a lawn tent for the children is to take a large umbrella such as used on delivery wagons and drive the handle into the ground deep enough to hold it solid.  Fasten canvas or cotton cloth to the ends of the ribs and let it hang so that the bottom edge will touch the ground.  Light ropes can be tied to the ends of the ribs and fastened to stakes driven in the ground in a tent-like manner to make the whole more substantial and to stand against a heavy wind.  This makes an exceptionally fine tent, as the umbrella

[Illustration:  Lawn Tent Complete]

is waterproof; also, there is more room to stand up in than in a tent that is in the shape of a wigwam.  —­Contributed by J.A.  Whamer, Schenectady, N. Y.

** How to Make a Windmill of One or Two Horsepower for Practical Purposes [399]

A windmill for developing from 1/2 to 2 hp. may be constructed at home, the expense being very small and the results highly satisfactory.

The hub for the revolving fan wheel is first constructed.  One good way to get both the hub, lining, shaft and spokes for the blades, is to go to a wheelwright’s and purchase the wheel and axle of some old rig.  There are always a number of discarded carriages, wagons or parts thereof in the rear of the average blacksmith’s shop.  Sometimes for half a dollar, and often for nothing, you can get a wheel, an axle, and connected parts.  Remove from the