"When ye see a cloud rise out of the west straightway ye say, There cometh a shower; and so it is. And when ye see the south wind blow, ye say there will be heat; and it cometh to pass."—Luke xiii.

711. Why are there Reaumur's Thermometers and Fahrenheit's Thermometers?

Because their inventors, after whom they are named, adopted a different system of notation, or thermometrical marks; and as their thermometers have been adopted by various countries and authors, it is now difficult to dispense with either of them.

Fig. 22.—THE THERMOMETERS OF REAUMUR AND FAHRENHEIT COMPARED.

We have combined the two (see [fig. 22].) The diagram will, we have no doubt, prove exceedingly useful to scientific readers and experimentalists. There is also another system of notation, adopted by the French, called the centigrade, but it is not much referred to in Great Britain. In the centigrade thermometer 0 zero is the freezing point, and 100 the boiling point. Fahrenheit's scale is generally preferred. Reaumur's is mostly used in Germany. Of Fahrenheit's scale 32 is the freezing point, 55 is moderate heat, 76 summer heat in Great Britain, 98 is blood heat, and 212 is the boiling point. Mr. Wedgwood has invented a thermometer for testing high temperatures, each degree of which answers to l30 degrees of Fahrenheit. According to his scale cast iron melts at 2,786 deg.; fine gold at 2,016 deg.; fine silver 1,873 deg.; brass melts at 1,869 deg.; red heat is visible by day at 980 deg.; lead melts 612 deg.; bismuth melts 476 deg.; tin melts 412 deg.; and there is a curious fact with regard to the three metals, lead, bismuth, and tin, that if they are mixed in the proportions of 5, 8, and 3 parts respectively, the mixture (after previous fusion) will melt at a heat below that of boiling water.