These are undated sequences for lectures and papers, some belonging to the Cambridge period and probably contemporary with the material at MS. Eng. misc. c. 870/B.5 - MS. Eng. misc. c. 872/B.7 (see especially MS. Eng. misc. c. 425/C.3) but with later additions and updatings.

The material was received grouped under the three main headings of thermodynamics, statistical mechanics and relativity and these have been retained, though it is clear from Milne's descriptive titles for some of his notes that they no longer necessarily correspond to their original state. MS. Eng. misc. b. 426/C.58 is a later analysis of a statistical problem posed by Milne.

Some sequences of notes are paginated by Milne, others were clipped together and have been retained in Milne's order. Sometimes he used the backs of examination scripts or class exercises for his notes, but much of the material is written on the cream-laid large quarto paper used for the 1920s lectures. Additional pages and later work are usually on smaller format paper.