446 



Popular Hcience Monthly 



T 



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. 



Magnet Winder 



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. 



