Part 15 (1/2)

APPARATUS 132

[Illustration: Fig 106]

_233 Resistance Coils_ Fig 106 The construction of one coil is given in App 131 To have the set of coils so that they can be easily used, place the spools upon a base which, in the model, is 8-1/2 4 7/8 in

The spools are 1-3/4 in apart, center to center, and should be glued to the base Fig 106 is a plan of the apparatus U, V, etc, are binding-posts like App 46 The figures between them sho many Ohms resistance there are in the coil above The coils A, B, C, D, and E are wound respectively for 1, 2, 2, 5 and 10 Ohe, for exa 106), the resistance added will be but 1 Ohm; if you join with U and W, the coils A and B will be in the circuit and make 3 Ohms resistance; if V and X, 4 Ohms; if V and Y, 9 Ohms; if U and Z, the whole, or 20 Ohms

APPARATUS 133

_235 Resistance Coils_ For use in soths, etc, of wires (See text-book), it is very handy to have coils(The meter is a French unit of measure and represents 393705 of our inches)

Gerreater resistance than copper wire of the sath

(a) Make a coil (See App 131 for1 meter of No 30 German-silver wire

(b) Make a coil with 2 meters No 30 German-silver wire

(c) Make one with 2 meters of No 28 German-silver wire

(d) Make one with 20 meters of No 30 copper wire

The above wire must be insulated if it is to be wound upon spools Bare wire ed on boards or racks so that the current may not be short circuited

CHAPTER XVIII

APPARATUS FOR STATIC ELECTRICITY

_236 Static or Frictional Electricity_ There areand instructive experiments in this branch of electricity All that can be done here is to explain a few pieces of simple apparatus to show the presence of static electricity, it being taken for granted that you kno to produce it, and that you have some book of simple experi the presence of static electricity

APPARATUS 134

_238 Thread Electroscope_ A piece of ordinary thread may be used for this purpose Tie one end of it to the back of a chair or other support

APPARATUS 135

_239 Pith-Ball Electroscope_ Fig 107 The pith froht and porous When this is tied to the end of a silk thread, we get the pith-ball electroscope, so much talked about in nearly every text-book on physics The upper end of the thread117 shows a book, lead pencil, and a sht to hold the pencil steady The thread is tied to one end of the pencil

[Illustration: Fig 107]

APPARATUS 136