Fahrenheit. —The freezing-point is taken as the thirty-second degree of the scale, and 180 degrees are made between that and the boiling-point, which therefore becomes 212°. The zero of Fahrenheit was supposed to represent the absolute zero, or lowest possible temperature.

Centigrade or Celsius. — The freezing-point of water is taken as zero, and boiling-point as 100°.

Reaumur. — The freezing-point of water is taken as zero, the boiling-point as 80°. A degree Centigrade is therefore greater than a degree of Fahrenheit as 9 is greater than 5; and a degree of Reaumur is greater, as 9 is greater than 4.

To reduce Fahrenheit degrees to Centigrade, subtract 32 from the given degree of Fahrenheit, and multiply the remainder by 5 and divide it by 9; (F. degrees — 32)5/9. To reduce Centigrade to Fahrenheit, multiply the given degree of Centigrade by 9 and divide the product by 5, then to the quotient add 32: (9/5 C.o +32).

To reduce Fahrenheit to Reaumur, subtract 32 from the given degree of Fahrenheit and multiply the remainder by 4 and divide by 9 : (F.°-32) 4/9

To reduce Reaumur to Fahrenheit, multiply the given degree of Reaumur by 9 and divide by 4, then add 32 : (9/4 R° + 32).

To reduce Reaumur to Centigrade, multiply by 5/4.