If you're friendly with the boy next door or in the house directly in back of you, it's a simple matter to rig up a message-carrier by means of a light rope or stout twine, a little box or tin can, and a couple of small pulley blocks.

To the upper windowsill of both houses, attach a small pulley block such as may be bought in any ten-cent or hardware store. (If the distance is not too great and a good stout cord is used, a large staple or even a bent-over nail may do for the cord to pass through.)

Run a double line through each pulley block and stretch the line taut between both houses. Then tie a little wooden box or tin can along the line.

When you want to send a written or code message, place the communication in the box or can and pull the string to carry it along to the other house. When it bangs gently against the sill, your friend hears it, opens the box and gets your message.

When your friend wishes to answer or to send you a message the process is reversed, he placing a message inside the box and pulling the string to carry it back to your house.

The whole arrangement is similar to the double clothesline-and-pulley used in the upper story of many two-family houses.