This theme can be found in three exercise books numbered with the Roman numbers III, IV, and V. They are written in black ink and use the pre-revolutionary spelling. Exercise books I and II have not been found, and the editors invented the title of the chapter. On the inside of the back cover of exercise book V there is the inscription "Spring (April) 1915," which, presumably, corresponds with the date of its completion. In the same exercise book the manuscript is designated as a talk. Here we publish selected fragments from the exercise books IV and V.