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Records of wind strength taken onboard Spanish and French ships during the 1750-1850 period have been digitized and examined using content analysis techniques to derive the equivalent wind strength in terms of the current Beaufort scale, this conversion being a key step in any attempt to compare ancient records with modern climatologies. During the analysis it was evident that Spanish and French officers used a great number of different terms to describe the wind force. However, when the records are analyzed and homogenized, a broadly common and essentially narrow vocabulary was identified, indicating that, at this period, a great effort had been made to regulate the maritime language. Using contemporary dictionaries and navigation manuals, an equivalence was established between the original wind force terms and the Beaufort scale.

We have compiled a meteorological database over the world's oceans by digitizing data from European ship logbooks of voyages in the period 1750-1854. The observations are carefully reviewed and transformed into quantitative data. The chief contents of the database are wind direction and wind force information, from a period without standardized scales. It is found that the information content of these so-called non-instrumental data is much higher than previously believed. The 105-year CLIWOC database extends existing meteorological world ocean databases like ICOADS back in time by a full century.

Meteorological observations made on board ships prior to 1854 have until now been overlooked in climatological research largely as a result of the lack of rigorous abstraction and treatment criteria. However, the CLIWOC project has shown that millions of potentially valuable observations have been preserved throughout Europe in the many logbooks that were prepared by officers in the navies of the great powers. Moreover these data can be used and treated in a fashion similar to today's ship-based instrumental observations. The most significant logbook collections are from Spain, the UK, the Netherlands and France. This paper describes the main archives where the logbooks can be found and provides an account of their contents and of the manner in which they were set out. The potential of this source is emphasised by the fact that whilst the CLIWOC project abstracted data for 300,000 days, nearly 90% of the European logbook collections have yet to be examined. This paper concludes with a discussion as to the direction of future studies in this important field.