Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity (1854)
Davis, Daniel · Boston : Palmer and Hall · leaf 269
8, the double helix,a a, is confined to the base board by three brass bands.The inner helix is composed of several strands oflarge insulated copper wire. The similar ends ofthese strands at one extremity of the helix are con-nected with the screw-cup c. Their other ends aresoldered to the middle… … motion by a concealed spring, is made to dip its endsalternately into the glass cups, G, G, wiiich are tocontain mercury. The cups being open at the bot-tom, the mercury is brought in connection with theouter brass bands, upon which they are fixed. Boththese bands are connected with a screw-cup c,…
