| RefNo | Title | Date |
| EC/1890/11 | Pickering, Percival Spencer Umfreville: certificate of election to the Royal Society | |
| IM/003582 | Pickering, Percival Spencer Umfreville | nd |
| IM/Maull/003581 | Pickering, Percival Spencer Umfreville | 1893 |
| NLB/4/1109 | Copy letter from Herbert Rix, to Percival Spencer Umfreville Pickering, Fellow of the Royal Society | 19 January 1891 |
| NLB/10/782 | Copy letter from Theodore E James, to Messrs Harrison & Sons | [February 1895] |
| NLB/13/783 | Copy letter from Robert William Frederick Harrison, to Percival Spencer Umfreville Pickering, Fellow of the Royal Society, Harpenden, Hertfordshire | 24 November 1896 |
| NLB/13/786 | Copy letter from Robert William Frederick Harrison, to Richard Tetley Glazebrook, Fellow of the Royal Society | 25 November 1896 |
| NLB/16/192 | Copy letter from Robert William Frederick Harrison, to S P [P S] Pickering, Fellow of the Royal Society | 16 February 1898 |
| NLB/19/160 | Copy letter from Robert William Frederick Harrison, to Percival Spencer Umfreville Pickering, Fellow of the Royal Society, Harpenden, Hertfordshire | 3 July 1899 |
| NLB/22/197 | Copy letter from Robert William Frederick Harrison, to [Percival Spencer Umfreville] Pickering, Fellow of the Royal Society | 20 March 1901 |
| NLB/23/1/316 | Copy letter from Theodore E James, to Percival Spencer Umfreville Pickering, Fellow of the Royal Society | [24 October 1901] |
| NLB/35/148 | Copy letter from Archibald Geikie, to Percival Spencer Umfreville Pickering, Fellow of the Royal Society | 26 April 1907 |
| NLB/36/554 | Copy letter from Archibald Geikie, to Spencer Percival Umfreville Pickering, Fellow of the Royal Society | 14 November 1907 |
| NLB/44/45 | Copy letter from Robert William Frederick Harrison to Spencer Pickering FRS | 26 April 1911 |
| NLB/51/794 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society to Percial Spencer Umfreville Pickering FRS | 1 July 1915 |
| NLB/52/144 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society to Spencer Percival Umfreville Pickering FRS | 23 September 1915 |
| NLB/53/290 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to [Percival] Spencer [Umfreville] Pickering, Esq., FRS | 29 June 1916 |
| NLB/54/63 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to [Percival] Spencer Pickering Esquire, FRS | 31 January 1917 |
| NLB/54/310 | Copy letter from Arthur Schuster, Secretary of the Royal Society; to [Percival] Spencer Umfreville [Pickering] Esquire, FRS | 30 March 1917 |
| NLB/54/146 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Professor [Hugh Longbourne] Callendar, Chairman of the Physics and Chemistry Committee and FRS | 17 February 1917 |
| NLB/54/249 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Professor [Hugh Longbourne] Callendar, Chairman of the Physics and Chemistry Committee and FRS | 16 March 1917 |
| RR/23/74 | Referee's report by Alexander Scott, on a paper 'Problems bearing on residual affinity' by Percival Spencer Umfreville Pickering | February 1917 |
| NLB/59/62 | Copy letter from Edwin Deller, Assistant Secretary of the Royal Society; to [Percival Spencer Umfreville] Pickering Esquire, FRS | 13 July 1920 |
| NLB/55/509 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to [Percival Spencer Umfreville] Pickering, FRS | 02 May 1918 |
| NLB/55/449 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to [Percival] Spencer Pickering Esq., FRS | 09 April 1918 |
| NLB/60/760 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Messrs Beechcroft, Hay & Ledward; 9 Theobald's Road, London, W.C.l. | 4 April 1921 |
| RR/23/72 | Referee's report by Frederick George Donnan, on a paper 'Problems bearing on residual affinity' by Percival Spencer Umfreville Pickering | 1916 |
| NLB/61/582 | Copy letter from Frederick Alexander Towle, Assistant Secretary of the Royal Society; to Dr. [Edward John] Russell, FRS | 10 August 1921 |
| NLB/64/465 | Copy letter from David Prain, Treasurer of the Royal Society; to Mrs. [Percival] Spencer [Umfreville] Pickering; Woolacombe, Devon | 18 April 1923 |
| NLB/62/554 | Copy letter from David Prain, Treasurer and Vice President of the Royal Society; to Messrs Beachcroft, Hay & Ledward; 9 Theobald's Road, London, W.C.l. | 9 March 1922 |
| NLB/64/918 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Messrs. Beachcroft, Hay and Ledward, London, W.C.1 | 10 July 1923 |
| NLB/64/804 | Copy letter from David Prain, Treasurer of the Royal Society; to Messr Beachcroft, Hay & Ledward. | 21 June 1923 |
| NLB/60/750 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Messrs Beachcroft, Hay & Ledward; 9 Theobalds Road, W.C.l. | 23 March 1921 |
| NLB/69/462 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Prof [Arthur] Harden, FRS | 22 April 1926 |
| NLB/70/794 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Professor [Henry Edward] Armstrong, FRS | 26 September 1927 |
| NLB/68/325 | Copy letter from James Hopwood Jeans, Secretary of the Royal Society; to Professor [Henry Edward] Armstrong, FRS | 18 June 1925 |
| NLB/5/57 | Copy letter from Herbert Rix, to Spencer Pickering, Fellow of the Royal Society, Harpenden, Hertfordshire | 2 March 1891 |
| NLB/62/221 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Sir David Prain, Treasurer and Vice President of the Royal Society | 5 January 1922 |
| RR/23/73 | Referee's report by William Jackson Pope, on a paper 'Problems bearing on residual affinity' by Percival Spencer Umfreville Pickering | November 1916 |
| NLB/52 | New Letter Book volume 52, copy letters sent from Royal Society administration | 9 July 1915-8 March 1916 |
| RR/15/267 | Referee's report by Percival Spencer Umfreville Pickering, on a paper 'Some physical properties of nitric acid solutions' by Victor Herbert Veley and J J Manley | March 1901 |
| RR/14/246 | Referee's report by Percival Spencer Umfreville Pickering, on a paper 'Researches in absolute mercurial thermometry' by Sidney A Sworn | 17 July 1899 |
| RR/13/43 | Referee's report by Percival Spencer Umfreville Pickering, on a paper 'Complete freezing-point curves of binary alloys containing silver or copper, together with another metal' by Charles Thomas Heycock and Francis Henry Neville | July 1896 |
| RR/13/153 | Referee's report by Percival Spencer Umfreville Pickering, on a paper 'Experimental proof of van 't Hoff's law' by Meyer Wildermann | 2 December 1896 |