Part 6 (1/2)

APPARATUS 64

_85 Co 39 With a sharp knife h a flat cork Into the cut push a short length of

In the illustration the spring is shown partly removed from the cut

Float the cork

APPARATUS 65

_86 Co 40 Stick a pin, P, into a pasteboard, cork, or wooden base, B Bend a piece of stiff paper double, as shown, and then stick through it, on each side, a -needle, S N The north poles of the needles should be at the same end of the paper Why?

Balance the paper upon the pin-pivot, and see it fly around to the north and south

[Illustration: Fig 39]

[Illustration: Fig 40]

[Illustration: Fig 41]

APPARATUS 66

_87 Conetic needle that is always ready for use The support is h the top of a wooden pill-box, which should be about 1-3/4 in in diaives plenty of roo, it will not be possible to put the bottoether when you want to put the coth, so that the netic needle can be safely put away in the closed pill-box

88 The ”Needle,” that is the short baris already quite hard and brittle, it ths It is always better tothe, each about 1-1/2 in long Bend theood dent, not a hole, should be made at the center of each to keep them upon the support or pin-point A ”center punch,” not too sharp, is the best tool to use, but a slight dentis first annealed or softened (See App 21) Do not place the spring directly upon iron or steel when ht injure the point of the punch, and the dent would not be deep enough Fig 42 shows a good way to s Place 2 or 3 layers of copper or lead between the anvil and the spring A haive easily, a good dentthe punch or nail with a ha it, it should be hardened again (App 21) before netisnetis 42]

89 Balancing After a dent has beenupon its support so that the pin-point shall be in the dent It will, no doubt, need balancing If one end is but slightly heavier than the other, the spring hter end shall become a north pole This will then tend to ”dip” andhorizontally If one end is netized and then balanced by cutting little pieces fro the lighter end with thread, which may be wound around it The finished co very freely, and should finally co back and forth several times

APPARATUS 67

_90 Glass-Covered Compass_ A perspective view of this apparatus is shown in the tangent galvanometer (See Index) The outside band, E, is made of thick paper, 1 in wide, and with such a dialass In this4 in in diameter Four pasteboard strips were sewed to the inside of the paper band E They wereupon them, would be near the top of E

The needle should be not over 1 in long, if it is to be used in the galvano slender paper pointer should be stuck to the top of the needle Be careful to have the co freely A circle graduated into 5-degree spaces should be fastened under the needle

_91 Astatic Needles_ In the -power has been quite strong By pointing-poearound to the N and S In App 65 the 2 needle -power, because they helped each other For sonetic needle is required which has but little pointing-power; in fact, to detect the presence of very feeble currents by -power the better Can you think of any way to arrange App 65 so that it shall have very little pointing-power?

APPARATUS 68

_92 Astatic Needle_ Fig 43 Turn one of the needle nets of App 65 end for end, so that the N pole of one shall be at the same end of the paper as the S pole of the other You can see that by this arrangenetic field still renets, otherwise this coalvanoth, the less the pointing-power of the co 43]

[Illustration: Fig 44]

APPARATUS 69

_93 Astatic Needle_ Fig 44 Magnetize ting-needles as equally as possible, by rubbing thenet an equal nu from a piece of fine copper wire, say No