Copy letter from Robert William Frederick Harrison to Professor S [Silvanus] P [Phillips] Thompson FRS 'Dear Dr Thompson, Many thanks for your letter.Your suggested demonstration of the use of polarised light for showing strains in structure would, I am sure, be most interesting and appropriate; but this time the difficulty arises that the Soiree Committee, on account of the large influx of foreign guests who are to be invited in connection with the Darwin celebrations, have decided to have no meeting room demonstrations, but to use that room to relieve the refreshment and reception space. Would it be out of the question to show your polarised light experiments somewhere upstairs?' 24 May 1909