The thermometer is an instrument for measuring the heat or temperature of bodies by the regular expansion of mercury or alcohol in a graduated glass tube. Halley proposed the substitution of mercury for alcohol in 1697. The thermometers usually employed are Fahrenheit's, the Centigrade and Reaumur's, the first invented in 1726, and the two others soon afterwards.

The following table is interesting as a comparison of the three thermometers:

Reaumur.

Centigrade.

Fahrenheit.

Freezing point

0

0

32

Vine Cultivation

8

10

50

Cotton cultivation

16

20

68

Hatching eggs

32

40

104

40

50

122

48

60

140

56

70

158

64

80

176

72

90

194

Water boils

80

100

212

Ice melts at 32°; temperature of globe, 50°; blood heat, 98°; alcohol boils, 174°; water boils, 212c°; lead melts, 594°; heat of common fire, 1,140°; brass melts, 2,233°; iron melts, 3,479°.

To convert one thermometer into another, observe the following rules:

To convert Fahrenheit into Centigrade - Deduct 32°, multiply by 5 and divide by 9.

To convert Fahrenheit into Reaumur - Deduct 32°, divide by 9 and multiply by 4.

To convert Centigrade into Fahrenheit - Multiply by 9, divide by 5 and add 32°.

To convert Centigrade into Reaumur - Multiply by 4 and divide by 5.

To convert Reaumur into Centigrade - Multiply by 5 and divide by 4.

To convert Reaumur into Fahrenheit - Multiply by 9, divide by 4 and add 32°. ______