Page:Evolution of the thermometer.djvu/78

 derivation we must bear in mind that the ratio between the capacity of the bulb and of the stem is constant for equal increments of heat.

then: 161.7 : 10,000 = 180 : x, and x = 11,124.

(Fahrenheit's figure 161.7 is, however, erroneous, it should be 181.53.)

A number of Fahrenheit's original thermometers are preserved in European institutions; two are in the physical cabinet, Leyden, one 653 mm. long is graduated from &minus;4° to 600°, the other one is 232 mm. long and has a scale from &minus;4 to 100°. Both are filled with mercury. Comparison with a modern standard thermometer shows that the freezing-point of water in the larger one is 34.2°, and in the smaller 34.1°. The Real Gymnasium of St. Peter, in Danzig, treasures one of Fahrenheit's early thermometers; it is filled with alcohol, measures 110 mm. in length, and has attached in a glass tube a paper scale graduated from