Reanalyses of Maskelyne's tidal data at St. Helena in 1761

The construction of an electronic data set of the tidal measurements made at St. Helena in 1761 by Nevil Maskelyne is described. These data were first analysed by Cartwright (1971, 1972) in papers which have importance within studies of changing tides. However, Cartwright's data files were never archived for the benefit of other researchers, demonstrating that “old data” at risk can sometimes take the form of electronic rather than paper records. In the present paper, the newly digitised Maskelyne data have been reanalysed by several techniques in order to obtain an updated impression of whether the tide has changed at that location in over two and a half centuries. This new data set may be found via https://doi.org/10.5285/e66db85a-eaae-6665-e053-6c86abc0bfb9 (Woodworth and Vassie, 2022). Our main conclusion, consistent with that of Cartwright, is that the major tidal constituent (M2) has changed little. However, the results of the various techniques demonstrate how difficult it is to obtain reliable conclusions for the smaller constituents.