A packet of letters and other items sewn together into one volume and entitled 'The Rev Mr Maskelyne's Letters, relating to the transit of Venus in 1761 and 1769 &c &c'.

1. Maskelyne to Charles Mason giving instructions on observing Venus' transit and financial arrangements on board the 'Sea Horse', addressed c/o Captain Smith, 29 November 1760.

2. Translations by Maskelyne of two papers by Alexandre Pingré:

i. 'Memoires de l'Academic Royales des Sciences', 1761, p. 437, concerning Mason's Cape observations of Venus.

ii. 'Memoires de l'Academic Royales des Sciences', 1763, p. 354, casting doubts on Mr Dixon's observations as communicated to Mason.

3. Maskelyne to Mason 'at Robert Williams, Teacher of Mathematics, Tetbury, Gloucestershire', 31 January 1769, regarding travelling arrangements for Mason in Ireland for observing the transit of Venus.

4. Maskelyne to Mason enquiring about his failure to respond, 7 February 1769, sent to Robert Williams, teacher of mathematics, Tetbury, Gloucestershire.

5. Maskelyne's instructions for observing the transit of Venus for 1769, with diagrams.

6. 'Directions to be observed by Mr Charles Mason with respect to his making Astronomical Observations in the North west parts of Ireland', 22 February 1769: eight instructions by Maskelyne for fixing the place of the observation and for observing the transit of Venus.

7. Maskelyne to Mason at Cavan, near Strabane, County Donegal, near Londonderry, Ireland, 8 May 1769, giving further instructions on observational technique and Mr Shelton's reasons for a clock spring breakage.

8. Maskelyne to Mason at Cavan, 23 May 1769, concerning a solar eclipse to be observed shortly after the transit of Venus.

9. Maskelyne to Mason at Cavan, 24 June 1769, concerning the success of Mason's observations of the transit of Venus and settling the longitude for these observations by occultations of small stars.

10. Maskelyne to Mason at Cavan, 7 August 1769, concerning settling the longitude of the Irish observations, and the results of other astronomers of Venus' transit, with comments on their poor quality.

11. Maskelyne to Mason at Cavan, 7 September 1769, concerning the 4 foot transit instrument and cometary observations.

12. Maskelyne to Mason at Cavan, 6 October 1769, concerning progress in settling the longitude at Cavan, occultations of stars, the whereabouts of the transit instruments, and cometary observations.

13. Maskelyne to Mason at Cavan, 9 November 1769, concerning cometary observations, the technique employed in making them, and Maskelyne's pleasure at the results.

14. Maskelyne to Mason at Mr Burn's, near the White Heart, Newington, Bucks, undated, concerning instructions for comparing the 1761 transit of Venus observed at the Cape with that observed in Ireland in 1769.

15. Maskelyne's computations for finding the apparent time of the external contact, etc., at Cavan, written in the hand of Charles Mason, with a few calculations on the longitude of Greenwich.