In Fahrenheit's thermometer, which is universally employed in this country and Great Britain, the freezing point of water is placed at 32°, and the boiling point at 212°, and the number of intervening degrees is 180.

The Centigrade thermometer, which has long been used in Sweden under the name of Celsius's thermometer, and is now most generally employed on the continent of Europe, marks the freezing point zero, and the boiling point 100°.

In Reaumur's thermometer, used in France before the revolution, the freezing point is at zero, and the boiling point at 80°.

In De Lisle's thermometer, used in Russia, the graduation begins at the boiling point, which is marked zero, while the freezing point is placed at 150°.

From the above statement it is evident that 180 degrees of Fahrenheit are equal to 100° of the centigrade, 80° of Reau-mur, and 150° of De Lisle; or 1 degree of the first is equal to of a degree of the second, 4/9 of a degree of the third, and 5/9 of a degree of the last. It is easy, therefore, to convert the degrees of one into the equivalent number of degrees of the other; but in ascertaining the corresponding points upon the different scales, it is necessary to take into consideration their different modes of graduation. Thus, as the zero of Fahrenheit is 32° below the point at which that of the centigrade and of Reaumur is placed, this number must be taken into account in the calculation. The following propositions will embrace all the cases which can arise in relation to the three last-mentioned thermometers. That of De Lisle is seldom or never referred to in works which are read in this country.

1. If any degree on the centigrade scale, either above or below zero, be multiplied by 9 and divided by 5, or if any degree of Reaumur above or below zero be multiplied by 9 and divided by 4, and to the quotient be added 32, the product in either case will be the exact number of degrees Fahrenheit.

2. Subtract 32 from any number of degrees of Fahrenheit's scale, multiply by 5 and divide by 9, the product will give the corresponding point on the centigrade', if multiplied by 4 and divided by 9, the product will give the corresponding point on the scale of Reaumur.)

3. Any degree of the centigrade multiplied by 4 and divided by 5, will give the corresponding degree of Reaumur; and conversely, any degree of Reaumur multiplied by 5 and divided by 4, will give the corresponding degree of the centigrade.

Fig. 357. - Thermometer.

Comparative table of degrees of the celsius, reaumur and Fahrenheit Thermometers.