[22]. Vide [note 14].

[23]. Vide [note 15].

[24]. Vide [note 16].

[25]. Vide [note 17].

[26]. Vide note 19.

[27]. Vide note 18.

[28]. Vide note 40.

[29]. Sichel—a German word meaning a crescent or a scythe. The original term is retained as there is no suitable English equivalent.

[30]. Planck, Zur Dynamik bewegter systeme, Ann. d. physik, Bd. 26, 1908, p. 1.

[31]. H. Minkowski; the passage refers to paper (2) of the present edition.