Secure a piece of window glass, 4-1/2 in. by 3-1/8 in. that is to be used as the front.  Before assembling the case cut on the inner surface of the pieces forming the sides and the lower end, a groove just wide enough to take the glass and 1/16 in. in depth.  The outer edge of this groove should be 3/8 in. from the outer edge of the frame.  After the case is fastened together there should be a slot between the piece forming the upper end and the piece that serves as a finish at the top, that will allow the glass to be slipped into place.  A small strip of wood should be tacked over this slot, after the glass is put in place, to prevent the dust and dirt from falling down inside of the case.

The piece upon which the works are to be mounted may be fastened in place by means of four round-headed brass screws that pass through the sides of the case.  It should be fastened about 1/2 in. back of the glass front.  The back may be fastened inside of the case in a similar manner.

Cut two pieces, from some sheet brass, whose dimensions correspond to those of Fig. 10.  These pieces are to be used in supporting the case by means of some small screws.  Fasten three binding-posts, that are to form the terminals of the annunciator, on the top of the upper end of the case.  Mark one of these binding-posts C and the other two Ll and L2.  Connect one terminal of each of the magnet windings to the post marked C and the other terminal to the posts Ll and L2.  You can finish the case in any style you may desire.  Often times it is desirable to have it correspond to the finish of the woodwork of the room in which it is to be placed.  The distance the point of the indicator will move through depends upon the distance between the cores of the magnets and the distance of the armature from these cores.  These distances are often times such that the indications of the cell are not very definite.  If the armature is moved too far from the cores there is not sufficient pull exerted by them when magnetized, to cause the position of the armature’ to change.

Mount on the shaft carrying the armature a small gear wheel.  Arrange another smaller gear to engage this on and fasten the indicator to the shaft of the smaller gear.  Any movement now of the armature shaft will result in a relative large movement of the indicator shaft.  Figure 11 shows the arrangement of the gears just described.

** How to Make a Steam Calliope [418]

Secure ten gas jet valves, the part of the gas fixture shown in Fig. 1, and prepare to place them in a piece of 1-in. pipe, 12 in. long.  This is done by drilling and tapping 10 holes, each

[Illustration:  Details of the Calliope]