Be careful about using some of the temperature data from the early 20th century. My grandfather's job was to record that data and he said the thermometers were always breaking or in the shade or sun or covered by leaves, etc. He said him and his co-workers would just guess at the numbers and say "it's close enough for government work". He also drank a bit. This was in the St. Louis and Cincinnati section.
Make your mind up: grandfather or great-grandfather?<quoted text>
My great-grandfather used to keep track of the temperatures back in the 1930's (before and after). He said the instrumentation was faulty (ie. broken thermometers). He and his co-workers would just guess at the temperatures and report them. They said it was "close enough for government work". He said he never would have guessed in a million years that people would be relying so much on the precise accuracy of those temperatures.
Sometimes they used the Draper thermometers.