[Note 456.1] The first London underground line; the Metropolitan line, opened in 1863. This lithograph shows the line near Paddington in that year. The reality would surely have been more filled with smoke.

[Note 456.2] "bussing is nowadays terribly slow" - The congestion in the streets of London was an important spur to the construction of the undergound

[Note 456.3] "steam through a tunnel, black as a funnel" - The use of steam locomotives resulted in tunnels full of filthy smoke-filled air. 

[Note 456.4] "And crowding for tickets was work precious hot" - The underground was crowded right from the outset.