for several purposes.  The sail is secured to the mast which is fixed into the body of the cart as shown.  The sail is linen fabric.  There are two crosspieces to aid in keeping the sail properly opened.  The steering arrangement is through the rear shaft.  The shaft is pivoted as in a hand-propelled cart, and the rod I extends from the middle connection of the shaft up to a point where the person seated on the wooden frame can handle it.  There is a brake arranged by making a looped piece J and hinging it as shown.  This piece is metal, fitted with a leather face.  The cord K is pulled to press the brake.  I marks the support for the mast underneath the body of the cart.  In a steady breeze this cart spins nicely along the roads.

** Replacing Ball Bearings [415]

Never change a single ball in a bearing.  Renew them all.

** How to Construct an Annunciator [416]

Oftentimes a single electric bell may be connected in a circuit so that it can be operated from more than one push button.  These push buttons are usually located in entirely different parts of the building and it is necessary to have some means of determining the particular push button that was pressed and caused the bell to operate.  The electric annunciator is a device that will indicate or record the various calls or signals that may be sent over the circuits to which the annunciator is connected.  A very simple and inexpensive annunciator may be made in the following way: 

Before taking up the construction of the annunciator it would be best to make a diagrammatic drawing of the circuit in which the annunciator is to operate.  The simplest circuit that will require an annunciator is one where the bell may be operated from either of two push buttons.  In this case the annunciator must be constructed to give only two indications.  Fig. 1 shows how the various’ elements of such a circuit may be connected.  B is an ordinary vibrating electric bell, M1 and M2 are the two electromagnets of the annunciator, A is a battery of several dry cells, and P1 and P2 are the push buttons from either of which the bell may be operated.

When the push button P1 is pressed the circuit is completed through the winding of the magnet M1 and its core becomes magnetized.  In a similar manner the core of the magnet M2 becomes magnetized when the push button P2 is pressed and the circuit completed through the winding of the magnet M2.

If an iron armature, that is supported by a shaft through its center and properly balanced, be placed near the ends of the cores of M1 and M2, as shown in Fig. 2, it may assume the position indicated by either the full or dotted lines, depending upon which of the magnets, M1 or M2, was last magnetized.  The position of this armature will serve to indicate the push button from which the bell was operated.  The magnets should be placed inside a case and the indication may be made by a pointer attached to the shaft, supporting the armature.