Early expedition records and explorer's logs are difficult to compare with modern measurements, as they are often short in duration. When making comparisons you have to remember they are essentially long runs of weather and the long-term change from the 19th century to the present is only about 1 deg C. This 1 deg C is small compared to weather variability. Attached is another paper on early US weather obs. There are a lot of issues to consider with early observations. I also tried years ago to look at early Antarctic weather obs from the explorer days. The day-to-day variability of Antarctic temperatures almost defeats anything being said, except perhaps in the Peninsula region.