By connecting the telephone receiver to the cell and at the same time having a short circuit a receiving station is made.  As the telephone offers a high resistance, part of the current will try to take the shorter high resistance through the needle.  If the waves strike across the needle, the resistance is less, and thus less current travels through the telephone receiver.  If the wave ceases, the resistance between the needle and the carbon is increased, and as less current will flow the short way, it is compelled to take the longer metallic way through the windings of the receiver, which will cause the clickings that can be heard.

** To Preserve Putty [121]

Putty, when left exposed to the air, will soon become dry and useless.  I have kept putty in good condition for more than a year by placing it in a glass jar and keeping it entirely covered with water.

** How to Make a Small Storage Battery [121]

The cell of a storage battery consists of two plates, a positive and a negative, made of lead and placed in a dilute solution of sulphuric acid.  Large batteries made of large cells have a great number of plates, both positive and negative, of which all positive plates are connected to one terminal and the negative plates to the other terminal.  The storage cell, as described below, is the right size to be charged by a few gravity cells and is easily made.

Secure a piece of 1-3/4-in. lead pipe, 5 in. long, and cut both ends smooth and square with the pipe.  Solder a circular disk of lead to one end, forming a cup of the pipe.  As this cup must hold the sulphuric acid it must be perfectly liquid-tight.  It is also necessary to get another lead pipe of the same length but only 3/4-in. in diameter.  In this pipe should be bored as many 1/8-in. holes

[Illustration:  Battery]

as possible, except for about 1 in. on each end.  One end of this tube is hammered together as shown at A in the sketch to make a pocket to hold the paste.  This, of course, does not need to be watertight.

A box of wood is made to hold the larger tube or cup.  This box can be square, and the corners left open around the cup can be filled with sawdust.  A support is now made from a block of wood to hold the tube, B, in place and to keep it from touching the cup C. This support or block, D, is cut circular with the same diameter as the lead cup C. The lower portion of the block is cut away so it will just fit inside of the cup to form a stopper.  The center of this block is now bored to make a hole the same size as the smaller lead pipe.  Place the lead pipe in the hole and immerse it in smoking hot paraffine wax, and leave it until the wood has become thoroughly saturated with the hot wax.  Use care to keep the wax from running on the lead at any place other than the end within the wood block.  Two binding-posts should be attached, one to the positive, or tube B, and the other to the negative, or tube C, by soldering the joint.