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��Popular Science Montlily
���At left, view of aerial screen system and secondary apparatus for collecting charges. At right, public demonstrating screen suspended thirty feet above ground by four poles
���At left, spectators experimenting with apparatus. One boy is waving a vacuum tube. At right, Prof. Thordarson examining his one million-volt, sixty-cycle transformer
��Engineers are of course interested in the details of construction of such a transformer, and some of the facts have been generously given by Mr. Thordar- son himself and by his assistant and o[)erating expert, Mr. A. S. Lindstrom. The laminated iron magnetic circuit is arranged on the "core" t\pe, with both primary and secondary windings grouped upon one leg only. Horizontal members are 120 ins. in length, the vertical ones 40 ins., their section being 16 ins. by 16 ins. Primary winding consists of 122 coils of 44 turns each of copper ribbon, .020 in. by .281 in. in section, i)iing the ef|ui\alent of a No. 12 romul wire. These coils are i)laced >4 in. apart, pairs being connected in series, lluii the 61 groups connected in parallel lor receiving the 2,20o-\-olt supiil)'. When assemi)led, the primary portion lormed a cylinder 67 ins. long, 23 ins. inside diameter, 28 ins. outside diameter. As a jirotection from i-iectrostatic surges
��the junctions between the pairs were connected to a heavy copper bar that was thoroughly "grounded" to frame and earth. Over the primary coils was a specially prejiared paper c>linder 92 ins. long, inside diameter 29^2 ins., outside 41 '2 ins., therefore 6 ins. thick. For the high \-oltage secondary wind- ing 190 separate coils were used, each adapted for 5,300 volts, being all connected in series. Each coil consists of 212 turns of aluminum foil, .008 in. L>y -135 i-' with three thicknesses of .006 in. paper between turns, and when finalK' assemliled forming a tube 71 ins. long, 43 ins. inside tiianieter, and 51 ins. outside diameter. The construction ot this secondary was of course the crucial |)art of the whole experiment, anil the ingenuity that was brought out to cope with the different problems is of the greatest credit to the designer and builder. In gciur.il, the principle of construction atlopted, that of breaking
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