The same period showed a quickening of interest in 'progressive tonality' as displayed in the music of Carl Nielsen, in which it plays a particularly significant role. In Nielsen's Fourth Symphony, for example, the initial tonal focus of D minor (clashing with C) issues at the end of the work in a firm E major. In the two-movement Fifth Symphony, more radical in this regard, the first movement begins in F and rises by fifths to a conclusion in G, while the second begins on B, with an opposing pull to F, and while tending towards A major works round instead, by a similar tritone opposition, to a triumphant close in E flat. The tonal workings of these symphonies were analysed with particular clarity by the British composer and writer Robert Simpson in his book "Carl Nielsen, Symphonist" (first edition 1952), which gave the whole conception of 'progressive tonality' something like popular currency in the English-speaking world; and similar principles, partly derived from Nielsen, infuse the tonal workings of Simpson's own early symphonies and quartets.