| RefNo | Title | Date |
| RR/7/18 | Referee's report by Isaac Todhunter, on a paper 'On the proof of the law of errors of observations' by Morgan William Crofton | 9 November 1869 |
| RR/7/240 | Referee's report by Isaac Todhunter, on a paper 'On the algebraical analogues of logical relations' by Alexander John Ellis | 7 June 1873 |
| RR/8/174 | Referee's report by Isaac Todhunter, on a paper 'On the conduction of heat in ellipsoids of revolution' by William Davidson Niven | 11 July 1879 |
| RR/8/173 | Referee's report by Isaac Todhunter, on a paper 'On certain definite integrals occurring in spherical harmonic analysis and on the expansion, in series, of the potentials of the ellipsoid and the ellipse' by William Davidson Niven | 14 May 1879 |
| EC/1862/15 | Todhunter, Isaac: certificate of election to the Royal Society | |
| RR/7/75 | Referee's report by Bartholomew Price, on a paper 'On Jacobi's theorem respecting the relative equilibrium of a revolving ellipsoid of fluid, and on ivory's discussion of the theorem' by Isaac Todhunter | 4 May 1870 |
| RR/7/74 | Referee's report by Arthur Cayley, on a paper 'On Jacobi's theorem respecting the relative equilibrium of a revolving ellipsoid of fluid, and on ivory's discussion of the theorem' by Isaac Todhunter | 19 February 1870 |
| RR/7/177 | Referee's report by Isaac Todhunter, on a paper 'Contributions to formal logic' by Alexander John Ellis | 1872 |
| RR/6/89 | Referee's report by Isaac Todhunter, on a paper 'On the theory of local probability, applied to straight lines drawn at random in a plane; the methods used being also extended to the proof of certain new theorems in the integral calculus' by Morgan William Crofton | 7 April 1868 |
| HS/17/354 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 11 July 1864 |
| HS/17/357 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 2 February 1866 |
| HS/17/352 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 5 November 1861 |
| HS/17/353 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 6 April 1864 |
| HS/17/355 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 21 July 1864 |
| HS/17/356 | Letter, from Isaac Todhunter to Sir John Herschel, dated at St. John's, Cambridge | 30 May 1865 |
| HS/24/54 | Copy letter, from Sir John Herschel to Isaac Todhunter, dated at Collingwood | 18 July 1864 |
| HS/24/116 | Copy letter, from Sir John Herschel to Isaac Todhunter, dated at Collingwood | 4 July 1865 |
| HS/24/37 | Copy letter, from Sir John Herschel to Isaac Todhunter, dated at Collingwood | 7 April 1864 |
| HS/24/139 | Copy letter, from Sir John Herschel to Isaac Todhunter, dated at Collingwood | 19 January 1866 |