In the first letter, dated 13 Mar 1928 and numbered 17 (38), Thomson discusses the work of M S Bartlett, in particular that the assumptions he makes about each person's ability in the unknown quality e will average zero over a number of persons.

He refers to specification equations, and his trouble with them, in particular that they are true for all persons, using Robinson Crusoe as an analogy to show the problems with this premise. Ledermann has made brief marginal notes highlighting passages he agrees or disagrees with.

In the second letter, dated 20 Mar 1938 and numbered 17a (38), Thomson states that he was dissatisfied with his previous letter, but having had no time to attend to it he has enclosed it and sent it as it is.

He informs Ledermann that he will meet him in London, and encourages Ledermann to stay in London for as long as he wants. He refers briefly to Ledermann's correspondence with Paul Horst, as well as Thurstone’s iterative process for finding commonalities.