| RefNo | Title | Date |
| IM/002279 | Howorth, Sir Heny Hoyle | nd |
| EC/1893/09 | Howorth, Sir Henry Hoyle: certificate of election to the Royal Society | |
| NLB/10/1006 | Copy letter from Herbert Rix, to Messrs Harrison & Sons | 22 March 1895 |
| NLB/8/414 | Copy letter from the Assistant Secretary [Herbert Rix], to Messrs Harrison & Sons | 23 October 1893 |
| NLB/11/799 | Copy letter from Herbert Rix, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 8 October 1895 |
| NLB/11/807 | Copy letter from Herbert Rix, to Messrs Dulau & Company, 37 Soho Square, W. | 9 October 1895 |
| NLB/11/764 | Copy letter from Herbert Rix, to Messrs Robarts, Lubbock & Company | 2 October 1895 |
| NLB/13/517 | Copy letter from Robert William Frederick Harrison, to Messrs Robarts, Lubbock & Company | 2 October 1896 |
| NLB/13/545 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Professor William Odling, and Dr John Rose Bradford, Fellows of the the Royal Society | 5 October 1896 |
| NLB/17/328 | Copy letter from Theodore E James, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 12 October 1898 |
| NLB/15/446 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 5 October 1897 |
| NLB/15/431 | Copy letter from Robert William Frederick Harrison, to Messrs Robarts Lubbock & Company, 15 Lombard Street, E.C. | [2 October 1897] |
| NLB/16/634 | Copy letter from Robert William Frederick Harrison, to Sir Henry Howorth, Fellow of the Royal Society | 9 May 1898 |
| NLB/25/400 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 30 October 1902 |
| NLB/25/390 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 28 October 1902 |
| NLB/29/579 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 8 November 1904 |
| NLB/25/829 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 8 January 1903 |
| NLB/27/501 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 9 October 1903 |
| NLB/29/484 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 24 October 1904 |
| NLB/29/695 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 25 November 1904 |
| NLB/33/494 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society, Cambridge House, Sheringham, Norfolk | 13 September 1906 |
| NLB/36/231 | Copy letter from Robert William Frederick Harrison, to Sir Henry Hoyle Howorth, Fellow of the Royal Society | 25 September 1907 |
| NLB/46/596 | Copy letter from Robert William Frederick Harrison, to Sir Henry [Hoyle] Howorth, Fellow of the Royal Society | 1 October 1912 |
| NLB/52/908 | Copy letter from [Robert William Frederick Harrison, Assistant Secretary of the Royal Society]; to Messrs Harrison & Sons | 8 March 1916 |
| NLB/59/759 | Copy letter from Edwin Deller, Assistant Secretary of the Royal Society; to Sir Henry [Hoyle] Howorth, FRS | 9 November 1920 |
| NLB/59/574 | Copy letter from Edwin Deller, Assistant Secretary of the Royal Society; to Sir Henry [Hoyle] Howorth, FRS | 20 October 1920 |
| NLB/65/141 | Copy letter from Alfred Hastings White, Assistant Librarian of the Royal Society; to H. S. Howorth Esq.; 45 Lexham Gardens, S.W. | 10 August 1923 |
| PC/1/14 | Press cuttings relating to the Royal Society: general | 7 April 1893-26 June 1896 |