Copy letter from Robert William Frederick Harrison to Professor H [Harold] A [Albert] Wilson, Fellow of the Royal Society 'My dear Sir, In reply to your letter of the 16th instant as to your short paper on the "Effect of hydrogen, &c" I much regret to find that it is due to an oversight in the office that it was not included in the December number of the Proceedings [of the Royal Society]. Such accidents I am glad to say rarely happen and it is very unfortunate that it should have occurred in this case. I can only express my regret and say that your short paper will be put in the number of Proceedings we are now making up.' 19 January 1909