162 



THE EEASON WHY. 



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 xui. 



THERMOMETER. 



Reaumtir. Fahrenheit. 



Fig. 22. THE THERMOMETERS OP 



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 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 130 degrees of Fahren- 

 heit. 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 1,8C9 

 deg. ; red heat is visible by day at 980 deg. ; 

 lead melts 61 2 dog. ; bismuth melts 476 deg. ; 

 tin melts 442 deg. ; and there is a curious 

 facj 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. 



712. What is the difference 

 between the thermometer and the 

 barometer ? 



In the thermometer the column 

 of mercury is much smaller than in 

 the barometer, and is sealed from 

 the air ; while in the barometer the 

 column of mercury is open at one 

 end to atmospheric influence. 



713. Why does the mercury 

 in the thermometer, leing sealed 

 up, indicate the external tem- 

 perature ? 



