| RefNo | Title | Date |
| EC/1886/14 | Unwin, William Cawthorne: certificate of election to the Royal Society | |
| IM/004701 | Unwin, William Cawthorne | nd |
| NLB/10/592 | Copy letter from Herbert Rix, to J B Mercer, Yew Bank, Lower Broughton Road, Manchester | 1 January 1895 |
| NLB/11/16 | Copy letter from Herbert Rix, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 3 April 1895 |
| NLB/11/401 | Copy letter from Herbert Rix, to Lord Rayleigh [John William Strutt] | 21 June 1895 |
| NLB/11/880 | Copy letter from Herbert Rix, to Professor William Cawthorne Unwin, Fellow of the Royal Society, 7 Palace Gate Mansions, Kensington, W. | 25 October 1895 |
| NLB/13/217 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 6 July 1896 |
| NLB/12/600 | Copy letter from Michael Foster, to Professor Charles Vernon Boys, Harold Baily Dixon, Rev Frederick John Smith and Professor William Cawthorne Unwin | 20 March 1896 |
| RR/15/186 | Referee's report by William Cawthorne Unwin, on a paper 'The elastic equilibrium of circular cylinders under certain practical systems of load' by Louis Napoleon George Filon | June 1901 |
| NLB/14/191 | Copy letter from Theodore E James, to Professor Michael Foster, Secretary, Royal Society | 19 January 1897 |
| RR/15/376 | Referee's report by William Cawthorne Unwin, on a paper 'A throw-testing machine for reversals of mean stress' by Osborne Reynolds and J H Smith | 20 April 1902 |
| NLB/15/5 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 3 June 1897 |
| NLB/15/57 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 15 June 1897 |
| NLB/16/622 | Copy letter from Robert William Frederick Harrison, to Professor Unwin, Fellow of the Royal Society, Palace Gate Mansions, 29 Palace Gate, Kensington | 9 May 1898 |
| NLB/17/566 | Copy letter from Theodore E James, to Messrs Harrison & Sons | 19 November 1898 |
| NLB/19/28 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 5 June 1899 |
| NLB/15/809 | Copy letter from Arthur William Rucker, to the Secretary to the Board of Trade, Whitehall, S.W. | 13 December 1897 |
| NLB/25/139 | Copy letter from Theodore E James, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 22 August 1902 |
| NLB/31/71 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 17 June 1905 |
| NLB/31/87 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 19 June 1905 |
| NLB/36/257 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 4 October 1907 |
| NLB/35/417 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 31 May 1907 |
| NLB/36/295 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society, Palace Gate Mansions, 29 Palace Gate, Kensington | 8 October 1907 |
| NLB/38/274 | Copy letter from Robert William Frederick Harrison, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 8 July 1908 |
| RR/21/142 | Referee's report by William Cawthorne Unwin, on a paper 'The determination of fatigue limits under alternating stress conditions' by C E Stromeyer | [April 1914] |
| RR/17/367 | Referee's report by William Cawthorne Unwin, on a paper 'The elastic limits of iron and steel under cyclical variations of stress' by Leonard Bairstow | 8 May 1909 |
| RR/20/138 | Referee's report by William Cawthorne Unwin, on a paper 'The determination of elastic limits under alternating stress conditions' by C E Stromeyer | 12 December 1913 |
| NLB/54/632 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Professor [William Cawthorne] Unwin, FRS | 9 July 1917 |
| AP/61/7/2 | Unpublished figures, experimental equipment and results by William Cawthorne Unwin | 1880 |
| RR/8/262 | Referee's report by Osborne Reynolds, on a paper 'On the friction of water against solid surfaces of different degrees of roughness' by William Cawthorne Unwin | 27 November 1880 |
| NLB/55/297 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Professor [William Cawthorne] Unwin, FRS | 18 February 1918 |
| RR/12/329 | Referee's report by William Cawthorne Unwin, on a paper 'The kinematics of machines' by T A Hearson | 26 May 1895 |
| RR/8/351 | Referee's report by Henry Charles Fleeming Jenkin, on a paper 'On the friction of water against solid surfaces of different degrees of roughness' by William Cawthorne Unwin | 20 February 1881 |
| RR/14/167 | Referee's report by William Cawthorne Unwin, on a paper 'An experimental investigation of the thermodynamical properties of superheated steam.— On the cooling of saturated steam by free expansion' by John H Grindley | nd [June 1899] |
| RR/10/331 | Referee's report by William Cawthorne Unwin, on a paper 'The rupture of steel by longitudinal stress' by Charles A Carus-Wilson | 26 April 1890 |
| NLB/64/849 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to the Director [Joseph Ernest Petavel, FRS] of the National Physical Laboratory | 29 June 1923 |
| NLB/71/908 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Prof. [William Cawthorne] Unwin, FRS | 5 December 1928 |
| NLB/71/801 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to the Secretary, Institute of the Civil Engineers, Great George Street, SW1 | 5 November 1928 |
| NLB/5/995 | Copy letter from Herbert Rix, to Professor William Cawthorne Unwin, Fellow of the Royal Society | 3 December 1891 |
| RR/11/70 | Referee's report by William Cawthorne Unwin, on a paper 'Note on the instability of India-rubber tubes and balloons when distended by fluid pressure' by Henry Reginald Arnulph Mallock | 17 April 1891 |
| NLB/11/159 | Copy letter from Dr Michael Foster, to Henry Cunningham, Home Office, Whitehall, S.W. | 4 May 1895 |
| NLB/11/132 | Copy letter from Michael Foster, to; Professor James Dewar, Professor William Cawthorne Unwin, Professor Charles Vernon Boys, Reverend Frederick John Smith and Harold Baily Dixon, Fellows of the Royal Society | 26 April 1895 |
| RR/15/332 | Referee's report by William Cawthorne Unwin, on a paper 'The fracture of metals under repeated alternations of stress' by James Alfred Ewing and J C W Humfrey | 29 August 1902 |
| RR/15/350 | Referee's report by William Cawthorne Unwin, on a paper 'Effects of strain on the crystalline structure of lead' by J C W Humphrey | 28 June 1902 |
| RR/15/52 | Referee's report by William Cawthorne Unwin, on the Bakerian lecture 'The crytalline structure of metals' by James Alfred Ewing and Walter Rosenhain | 19 July 1900 |
| RR/10/271 | Referee's report by William Cawthorne Unwin, on a paper 'On the conditions for effective scour in drain-pipes of circular section' by Henry Hennessy | 9 March 1889 |
| RR/13/273 | Referee's report by William Cawthorne Unwin, on a paper 'On the passage of heat between metal surfaces and liquids in contact with them' by Thomas Edward Stanton | 9 May 1897 |
| RR/15/99 | Referee's report by William Cawthorne Unwin, on a paper 'The kinetic accumulation of stress, illustrated by the theory of impulsive torsion' by Karl Pearson | 2 August 1900 |
| RR/13/93 | Referee's report by William Cawthorne Unwin, on a paper 'On the structure of metals, its origin and changes' by M F Osmond and William Chandler Roberts-Austen | 8 July 1896 |
| PP/10/59 | Paper, 'Note on some experiments on the viscosity of ice' by J F [John Frederic] Main | 1887 |
| PP/10/59/1 | Manuscript, 'Note on some experiments on the viscosity of ice' by J F [John Frederic] Main | 1887 |
| RR/12/414 | Referee's report by William Cawthorne Unwin, on a paper 'Iron and steel at welding temperatures' by T Wrightson | 15 March 1895 |
| AP/61/7 | Unpublished paper, 'On the friction of water against solid surfaces of different degrees of roughness' by W [William] Cawthorne Unwin | 1880 |
| AP/61/7/1 | Unpublished manuscript, 'On the friction of water against solid surfaces of different degrees of roughness' by W [William] Cawthorne Unwin | 1880 |
| MC/20 | Volume 20 of miscellaneous correspondence regarding business matters, sent to the Royal Society | 1905 |
| MC/20/453 | Letter from [William Cawthorne] Unwin, Palace Gate Mansions, 29 Palace Gate, Kensington, to [Robert William Frederick] Harrison | 6 June 1905 |