In the first letter, dated 12 Apr 1938 and numbered 21 (38), Thomson tells Ledermann about his trip to Dumfries and the Galloway coast, informing him of his travel plans for the next few weeks which include going to Munich and Vienna. He asks Ledermann to undertake editing work on The Factorial Analysis of Human Ability, in particular ensuring a second manuscript is up to date. Thomson also refers to the mathematical appendix he has completed and is sending on to Ledermann to ensure it is correct, and sends good wishes for Ledermann's tour.

In the second letter, dated 19 Apr 1938 and numbered 21a (38), Thomson informs Ledermann that he has sent the typed manuscripts of the Factorial Analysis of Human Ability to Moray House for him to pick up, and is currently getting the last chapter typed. He also refers to an unnamed cousin of Ledermann who is in some difficulty, and gives Ledermann the name of Sir Philip Hartog, who may be able to help him.

Also includes a postcard, dated 21 May 1938 and numbered 21b (38), in which Thomson tells Ledermann briefly about his travels in Czechoslovakia and Sweden, and the professors he met there, and lets him know when he will be in Glenapp.