Catherine Sutherland (Deputy Librarian (Pepys Library & Special Collections) Magdalene College, Cambridge CB3 0AG) quoted the diary entry to K. Blackwell on 26 May 2016):

"Went 4.30 pm to Russell’s lecture – “4 truisms, 1 radical mistake.  3 Witticisms, 7 pleasantries – great success”.  Huge crowd – grand manner."

The lecture was the first of Russell's series of William James Lectures at Harvard in the autumn of 1940. See Michael D. Stevenson, "'My Personal Ruin Passes Unnoticed': Russell, Harvard, and the 1940 William James Lectureship" (https://mulpress.mcmaster.ca/russelljournal/article/view/2887/2569).

The diary is in the I.A. Richards Papers. Pillay is Richards' wife.