Let us take the temperature of the boiling water be 100 degrees in Celsius scale and 180 degrees in Fahrenheit scale. That is, ‌
140−32
180
=‌
C
5
‌ Therefore, ‌5×108=9C,‌‌C=60‌‌deg‌‌C since, the temperature of boiling water is 100 deg C, the required fall is 100−60=40 degrees C. Hence, The fall in temperature as registered by centigrade thermometer is 40 degree Celsius.