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JANUARY 27, 1912 SCIENTIFIC AMERICAN SUPPLEMENT No. 1882 61

An Easily Constructed

Instructions for the Amateur Electrician

By Allan S. Dana

THE special advantage of thp Tesla coil, here described, in paraffine and allowed to cool. In this manner the for an 8/32 serew. One inch from the other end bore is that it is comparatively small and light. Therefore entire surface of the tube is covered with a coil of wire, a 7,4:-inch hole half way through the rod. These last, it can be rpadily carried from place to place. Most whose adjacent turns are separated by the thickness holes are to hold the ends of the glass rod, whif'h passes Tesla coils are immersed in oil but this is objectionablp of the paraffined thread. To the ends of this coil lO-imh through the eenter of the sef'ondary coil and is uSf'd as the oil leaks or slops over, and also greatly increasps lengths of No. 28 or No. 30 copper wire are soldered, to support it. By 8/32 machine screws passing UJI the weight of the illl,trument. Although the oil-immersed and melted beeswax poured over the joint to hold it from the under side of the base hoard through the coil is more efficient, a Tesla coil in air is more convenient fast to the cardboard tube. the entire coil of holes already bored 12% inehes apart and 10 inches and only slightly less efficient. The air Tesla coil to wire, applying two coats of thin shellac.. When this from the front, these hard rubber rods are held to the be described has the same advantage that a coil in oil ha,s dried. unwind the paraffinen threafl ann give one base and, in turn, support the glass rod whieh earries has-that of having a fluid between the the secondary coil. primary and secondary coils, so that, if a spark passes Cut two 5-inch pieces of Yrinch hard rubber rod, accidentally between them, the air or oil immediately and bore and tap each end for an 8/32 screw. At one fills np the gap made by the spark. A solid insulator end of eaeh rod a binding post is serewed on, while n. cannot be used because one spark between the primary screw passing up from the under side of the base holds and secondary would make a hole in the insulating each rod perpendicular to it. material and the spark would easily travel through Then the ends of the secondary coil are connectl'd this hole thereafter. Hence a coil should be in eithpr to the binding posts on the top of the hard rubber rods. oil or air. But if it is to be portable, air must be tlH' The eoil is now complete. If used with an induction insulator. coil on , it is best to screw the vibra­ Using this coil with a 4-inch induction coil, it gives tor up tight, so that it will not work, and use a chokl'­ a 5 �'1!-inch spark. This iF the longest spark possihlp coil in the primary circuit in order to cut down the with this instrument, because the spark has to travel current. Still better, a , closed core trans­ only a little over 5 �� inches to jump from the primary former, such as used to send in , to the secondary coil. Hence, if the rods where the spark may be used. The terminals of a medium-sized glass discharge is supposed to take place are separated by plate condenser are connected to the secondary tl'rmi­ more than 5 Y2 inches, tbe spark will not jump there, nals of the or induction coil. Then onl' hut will take the shorter patb to the primary coil. terminal of the transformer or induction coil is con­ The base of this coil is a piece of I-inch whitewood, nected to one end of the coil of large wire on the Tesla IIi inches by 15 inches, with its edges molded. Two and eoil. The other end of this coil of large wire, or primary coil, is connected to a spark gap, and the other end of one-quarter inches from the front and 12% inches IIOV, AC apart bore two holes which will allow an 8/32 machin<' the spark gap to the other end of the transformer or screw to pass through. Again, bore two holes of th{' induction coil. When the current is turned on and tIl(> same size 10 inches from the front and 12% inches spark gap and eondenser regulated, a harmless 5 y:!..ill(�h from each other. Also two holes of the same size 10 Choke coil spark will jump between wires placed in the binding inches from the front and 37,4: inches apart. Screw posts to which the ends of the secondary of the Tf'sln. four rubber tips, such as used on furniture to avoid coil are connected. scarring polished floors, to the under side of the bast A great many experiments may be made with this board at the corners. These will keep it from scratch­ coil. Geissler tubes can be lighted by holding one end ing polished tables. The base may now be painted. of the tube in the hand and presenting the other f'lld A black varnish gives a good finish. /ndl.lction COIl or to one terminal of the Tesla coil. When this is done, Next, wind six turns of No. 2 copper wire around transformer the electricity which lights the tube passes througl, a circular form so as to make a coil 10 inches in diameter. the person and still does not cause any sensation. But At each side of the coil, place two pieces of Y2-inch in these days of wireless telegraphs and telephonf's, oak, 1 by 4 inches, which are supplied with machim' the most interesting experiment from the layman's screws and nuts, and clamp the wires 3/16 of an inch standpoint is a wireless light. To make. this, hend apart hy means of these. The machine screw heads 4 feet of No. 14 B. and S. insulated copper wir(' should be toward the inside of the coil and must bl' to form a circle and co�mect a 2- battery lamp f'ountersunk until flush. At the bottom of the coil to the ends of this coil. If this coil is then moved near another strip of oak is used to clamp the whole coil to the Tesla coil while it is in operation , the lamp will to the base by means of machine screws passing through light, provided, however, that the primary coil of the the oak strip and the holes already bored in the basp Tesla and the coil of the wireless light are in the same hoard. This oak strip should be of Y2-inch oak, 1 by 4 or parallel planes. inches, with two holes for 8/32 screws, 37,4: inches apart. ] I ia;.:ra111 ,,!, ('''IIIH'dioll'' WI" Fittil1� 11]1 tilt' ']'(''']:1 ('oil. Many other experiments can be carried Ollt by mf'ans Il1a;':1'1I111 01' ('01l1H'CtiOIl" TOI' I" itti n� 11]1 thl' T!'slll Coil. Flatten the ends of this primary coil and hore in each of' this simple 'resla coil. ==--:.;=== a hole which will allow the binding post from the car­ A Passenger Cableway on Mont Blanc hon of an old dry battery to be put on and used as or two more f'oats of shellaf' to hold thf' wir!' onto the a terminal of the coil. f'ardhoard tllhe. n(' sur I' that no two turns of the eoil TOURISTS will soon be able to make the asl�f'nt, of The secondary coil is wound on a cardboard tube touf'h. EVl'ry turn must be separated from the next Mont Blanc by the aid of a suspended railway now 4% inches in diameter and 77,4: inches long. Cut two one by the width of the paraffincd thread. When in the course of construction, of which we puhlish disks of 3/S-inch wood to fit tigh tly the ends of th(' this is dry, pass a U-inch glass rod, ]2% inelws long, Illustrat.ions herewith. This is the seeond eahle Jill(' of tuhe and bore a X-inch hole in the ('enter of each disk. through the holes in the wooden disks in the end of tlw its kind to he inst.alled in Europe, a similar f�ahl(>way Monnt t.he tube 1·0 that it can he revc1ved and wind, .:ardhoard tube. having been built some ypars ago on the Wllttl'rhol'l1, side by side, a No. 36 single cotton-covpred copper From a %-inch hard rubber rod cut two pief'es 6 as described in the f;CIENTIFIC AMERICAN of May Rth, wire and a thread of 100 cotton. whkh has been soaked inehes long. In one end of each bore and tap a hole 1909.

Near View of tile Car. View l:lilowing Two Towers and a Spun of Cnble.

© 1912 SCIENTIFIC AMERICAN, INC.