Irish Famine (1740–41) affect economies, energy sources, and politics. Although no barometric or temperature readings for Ireland survive from the Great Frost, a scattered few records survive from Englishmen who made personal readings. The mercury thermometer was invented 25 years earlier by the German pioneer Daniel Gabriel Fahrenheit. Indoor values during January 1740 were as low as . The one outdoor reading that has survived was stated as "thirty-two degrees of frost." This did not include the effects of the wind chill factor, which would have been severe. This kind of weather was "quite outside the Irish experience," notes David Dickson, author of
Six's thermometer the mercury, and returning it to the horizontal. The Six's thermometer is known for separations in the mercury column, in particular after shipment, though accidental knocks have been known causes as well. Separations can usually be corrected by swinging the thermometer as is done to reset a mercury clinical thermometer; the centrifugal force forces the mercury together again. Should a marker become partly buried in the mercury, it can either be pulled up again with the magnet or exposed to an extreme temperature that leaves the marker uncovered. If a strong external magnet is used to pull up the markers