��Popular Hcience Monthly
��Inductio n Coil Large Enough for a Small Wireless
��Making an Induction Coil
^HE laboratory of the elec- trical experimenter is incomiilete with- out an influcliou coil, and in com- mercial work this device probably serves more pur- poses than any (ithor piece of elec- trical apparatus. A coil large enough tor a small wireless, and one which will make a spark big enough to ignite gunpowder some distance from the switch, can be made by any amateur, witii little expense.
Secure a tube of cardboard or hard rubber, i ft. long, with an outside diaiiicter of i in. Cut two pine blocks I in. thick and 6 ins. .square. Bore a
1 in. hole in the end of each block and slip the ends of the tube into these holes, tacking it to the wood from the inside. Appiv several coats of shellac to the whole arrangement, allowing each coat to tir\,' before adding the next. Binding posts or wooden screws are screwed into the upper edges of the blocks, as shown in the diagram.
The coil should next be wound. If a lathe is available, fasten the tube and blocks between centers, and the winding will be an easy matter; if not, it may be wound by hand, though the process is slow. For the primary coil use No. 20 double cotton-covered copper wire. Fasten one end to a binding post, and wind a layer evenly on the tube. Coat with shellac; add a layer of thin paper and shellac that. Repeat this process until four layers are wound, fastening the end of wire to the other binding post on the same block with the end started with. Wind on several la\ers of paper and coat libiTally with shillac This keeps out moisture, which is fatal to the proper working of the coil.
Wind the secondary coil with about
2 lbs. of No. 36 insulated co|)per wire. Proceed as with the |)rimary coil, but use the binding [josts at the op|M)site end of the tube. Shellac and paper arc
��applied as before; after the last layer of wire, add an extra coating of each.
The coil may be mounted on a wooden base, 14 ins. by 6 ins. by i in. Give it several coats of shellac. Kiln-dricxl wood is best for the whole apparatus, if obtainable. — P. J. McClute.
IX winding a magnet coil it is often a tedious job to get the la\ers smooth, especialK- if the wire is small. In the accompanying sketch is shown a device which o\ercomes this ditticult%-.
It consists of an ordinary hand-drill which is firmly held in the bench-vise.
The magnet spool is easily fastened in the chuck by using a long screw of the same thread as that intended for the magnet. By cutting off the head it may be held in the chuck as a regular magnet winder.— K. C. Meilloret.
���Device for Facilitating the Smooth Wind- ing of a Magnet Coil of Fine Wire
Utilizing Broken Marble Pieces
PIKCliS of broken marjile can often be purchased from the second-hand stores for a few cents and then cut and worked into excellent bases for support- ing wireless instruments. If such bases were purchased from the marble worker lhe\- would cost a great deal more.
The pieces of marble ma\- be sawed to shape by hand, using a strip of sheet-iron as a saw and common ri\'er sand as the abrasi\-e. To polish the edges use sand and water upon a piece of scrap marble or glass, and rub the piece to be (lolished owr the abrasi\e until the di'sired finish is produced.
Dry Cells and Their Voltage
THK ordinary dry cell should show a voltage of nearly one and a half and an instantaneous test-current of oviT lifliHMi amperes, if it is to be depended upon lor rinming an induction coil or similar iiislrument.