Came across these photos from the Digital Research Library of Illinois History Journal. May have been posted before, but cool to see where they came from! CD 181 "PLUTO"s here and there, was expecting to see nothing but CD 181s from what I had read prior. Close up of the upper left Pluto next page. Description copied below of the infrastructure from the article, 4,000 CD 181s

The total length of the subway, including the east and west subway under Machinery Hall, all the branches and approaches to the bridges, was 6,195 feet. The subway's wiring began in February 1893 and continued for about six weeks. It was found that there were so many arc wires for Manufactures building that had to be placed on the east wall of the east subway that it was necessary to run two wires on one insulator. For that purpose, a special two-wire insulator was designed and laid the glass insulation between the two wires. Wires were also arranged so that no two wires of different potential would come on the same insulator. The wiring of the subway required 4,000 of the special two-wire insulators and 20,000 of the regular single glass insulators. The subway contained 25 2-10 miles of power, 28 7-10 miles of incandescent and 51 miles of arc wires, making a total of 104 5-10 miles of wire for lighting and power transmission. Besides these were telephone and telegraph cables, fire alarms and police signal wires.