Part 12 (1/2)
179 The Base should be about 7 5 7/8 in Fasten three bent brass or copper strips to the base with brass screws to hold the chi the fit around the chi the Needle In the center of the box-cover is a sh this The upper end of the thread is wound around a screw-eye, which is screwed into the cover near one edge By turning the cover around, the needle can bethe screw-eye, the needle can be raised or lowered A s in the screw-eye, or you will be liable to split the wood
[Illustration: Fig 89]
181 Use This apparatus will indicate very slight currents; in fact, as feeble ones as the student will have occasion to experiment with, such as induced currents, currents of therly weak batteries (See text-book)
APPARATUS 116
_182 Tangent Galvanoalvano this apparatus The base is 5 4 7/8 in At its front end are three binding-posts The pasteboard band, G, is 1-1/4 in wide and 6 in in dia and 1-1/4 in wide, then bend it into the form of a circle There will be a lap of about 3 in, and you can ether at the lap
[Illustration: Fig 90]
183 The Coils maybe made of No 24 insulated copper wire, which should be wound on before fastening G to the base There are two separate coils, one having five turns and the other ten turns Leaving a 6-in
length, A, for connections, wind five turns of wire on to G, putting them on clockwise; that is, pass theht Tie thread around G and the wire to hold theether after you have five turns on, and cut a 6-in end, B Now begin with C, and wind on ten turns, bringing the end of theh G on each side of the coils, run twine, T, through them, and tie T on the outside of G Do this in three or four places, to fir Coils to Base The band and coils will not rest squarely upon the base, so cut two pieces of wood, E, about 2 1/4 1/4 in, to be put under G, one being on each side of the coil Make holes through the base, pass strong cord, H, through them, and over the inside of G, then tie under the base This should tightly squeeze E, and hold G upright and firm
185 The Connections A and B are the ends of the five-turn coil; C and D are the ends of the ten-turn coil If the battery-wires are connected with X and Y, the current will pass through five turns of wire; if connected with Y and Z, it will pass through ten turns; if with X and Z, the current will pass through the entire fifteen turns In this way the strength of the ulated, and its effect upon the ed
186 To Support the Needle, glue or seo strips, I, to G They must be in such a position that the poles of M will be as nearly as possible in a horizontal line drawn through the center of the circle, G After you have made M (App 66), and have found where the pieces, I, should be, fasten thelue a pasteboard strip, J, about 1-1/4 in wide Run a pin, P, up through the center of J to support M
187 The Magnetic Needle, M, should not be over 1 in long for this kind of an instru it) On the top of M should be fastened a light paper pointer or index, L The short end should beslim end will not over-turn M; that is, the pointer should balance itself It -wax If carefully balanced, the pointer can be
188 The Graduated Circle, K, is described (Index) With this you can tell through how rees the needle is deflected, when the current passes The strength of different currents can be co experialvanometer For clearness, the circle, K, is shown sh apart, K should be about 4 in in diameter The zero points should be at the front and back of the instrument, when a pointer is used on the needle
189 How to Use It For full explanations, and for the study of experialvanoet M exactly in the center of G; you cannot get the pointer exactly at right angles with M; hence, if you pass a certain current through the coils, and the pointer reads 20 degrees, you will find, if you reverse the current, h the coil in an opposite direction, that the pointer et the true reading, then, take the average of the thich in the case rees (See current reversers)
APPARATUS 117
_190 Tangent Galvano 91 The base consists of 2 parts, A and B It is not necessary to use two pieces if you have wood that is at least 7/8 in thick This is given as a suggestion in case you have nothing but thin boards By screwing B to A the base is -posts The base proper, A, is 8-1/2 5 1/2 in If you make this of 7/8 in stuff, you will not need B
The Back, C, is 10 8-1/2 1/2 in It is screwed to the base Do not use nails, as these affect the netic needle Find the center of C, and with this as a center, drao circles, (that is, the circumferences of two circles,) one 5 in in diameter to shohere to cut out a hole, H, and the other 7 in in dia on the spools, F
[Illustration: Fig 91]
The Spools, F, are glued to C If you have brass screws, these may be used instead of the spools; they should be left sticking out from C about 1 in Around the spools or screws, fasten a pasteboard band, G, on which to wind the wire G may be about 1 in wide; it should be kept in the circular forether where they lap (Read directions in App 116)
191 The Coils on this ) The first coil isjoined to the binding-posts, V and W The second coil has 5 turns of No 24 insulated copper wire, its ends being joined to W and X
The third coil has 10 turns of the same size wire, No 24, and is joined to X and Y The fourth coil has 20 turns of the saalvanometer for quite weak currents, it would be well to make a fifth coil of 20 turns of No 30 wire, and join it with Z and a new binding-post The ends of the coils are run through s to X, Y, etc This is not necessary, it -Posts are like App 43 Any other desired stylepreferred
The Hole, H, is 5 in in diameter It should be cut out about 1/2 in