Part 4 (1/2)

APPARATUS 39

_56 Switch_ Fig 25 By increasing the nu from them, a switch may be made to throw in one or more pieces of apparatus This variety of switch is useful in connection with resistance coils (Index) By joining the ends of the coils with the points 1, 2, 3, etc, more or less resistance can be easily thrown in by siht The uses of this will be again referred to

[Illustration: Fig 25]

Details The base of the one shown in Fig 25 is 4 5 7/8 in thick

The switch, E, is a band of 2 thicknesses of tin 5/8 in wide It is pivoted at F with a screw To the end of E is fastened a copper wire, which leads to the upper binding-post, X (App 46) The apparatus has 5 contact points, marked 1, 2, 3, etc These consist of brass screws and copper washers With F as a center draw the arc of a circle that has a radius of 4 in Place the screws 1, 2, etc, along this arc, and about 5/8 in apart, center to center; that is, the screws are all 4 in from F, and are, therefore, in the for-post, Y Suppose 4 pieces of apparatus, marked A, B, C, and D, be connected with 1, 2, etc, as shown These may be, for example, coils of wire to be used as resistance coils If the current enters at X, it will pass along at E and be ready to leave at Y, as soon as E touches one of the contact points If E be placed upon 1, the current will be obliged to pass through all of the coils, A, B, etc, before it can get to Y In this case the resistance will be greatest If E be now moved on to 2, only A will be cut out, and the total resistance reduced By placing E upon 4, but one coil, D, will be in the circuit When E is upon 5 the current will pass through the switch with practically no resistance This is the principle upon which current regulators work (Study resistance in text-book) When E is in the position shown in Fig 25 no current can pass

CHAPTER V

BINDING-POSTS AND CONNECTORS

_57 Binding-Posts_ are used to make connections between two pieces of apparatus, between two or more wires, between a wire and any apparatus, etc, etc They are used simply for convenience, so that the wires can be quickly fastened or unfastened to the apparatus There areforh so-posts, we shall give the-posts

APPARATUS 40

_58 Binding-Post_ About the simplest form is a screw, or a nail with a flat head The bare wire may be placed under the head of the screw or nail before forcing it entirely into the wood This will keep the end of the wire in place, and another wireit to the screw-head, or by placing it under the screw-head

APPARATUS 41

_59 Binding-Post_ Fig 26 This consists of a screw and a copper washer or ”bur” The screw is a ”round-headed brass” one, 5/8 in long, number 5 or 7 The copper burs are No 8, and fit nicely around the screws By using 2 burs instead of 1, several wires ether at one point Scrape the covering from the ends of the wires, and place the 26]

APPARATUS 42

_60 Binding-Post_ Fig 27 A coiled spring serves very well as a connector One end should be fastened to the apparatus, as shown, by cla it under a screw-head The other end of the coil should be pulled out a little, away fro in order to put the bare ends of wires between the turns Any number of wires placed between these turns will be pinched and electrically connected The coil should be about 1/2 in long and less than 1/2 in in dia stiff iron wire around a pencil The steel wire springs taken from old -shades are excellent for this purpose They ths with tinner's shears

APPARATUS 43

_61 Binding-Post_ Fig 28 Two copper or tin strips fastened at one end by a screw, the upper strip being bent a little at one end, make a connector that is useful for some purposes, where you want to make and break the connection frequently The bare end of the hich belongs to the apparatus is fastened under the screw-head The outside wire, or wires, to be connected are pushed between the strips of metal Another way is to fasten the outside wire to a strip of metal about 1/2 in

wide, and then push this between the strips shown in the figure The strips shown should be about 3/4 in wide and 1-1/4 in long

[Illustration: Fig 27]

[Illustration: Fig 28]

[Illustration: Fig 29]