THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXYIIL— Quartz as a Geologic Thermometer' by 

 Feed. Eugene Weight and Espee S. Laesen. 



The term temperature has been defined as "the degree of 

 hotness of a body measured according to some arbitrarily 

 chosen scale." * It is regarded as a - quality which can be 

 indicated in a thoroughly definite manner in terms of the 

 chosen scale. Heat, on the other hand, as something which 

 can be added to or taken away from matter, is treated as a 

 quantity, and the addition or subtraction of heat gives rise to 

 observed changes in temperature of a body. It is a fact of 

 observation that certain physical constants of matter change 

 slightly with the temperature, and these in turn have been 

 used to indicate the degree of hotness or temperature of 

 a body. Such temperature-indicating devices are called 

 thermometers and vary in type and construction with the tem- 

 perature ranges to be covered and the accuracy desired. The 

 most accurate method of expressing temperature is in terms 

 of the expansion of a perfect gas, and the gas thermometer is 

 the ultimate instrument for defining temperature at all points 

 of the scale. The gas thermometer, however, is less convenient 

 for ordinary use than other devices, and certain fixed points, 

 as the melting and boiling points of \vater and other chemically 

 pure substances, are first determined in terms of the gas ther- 

 mometer scale, and these in turn applied to other scales as 

 standard fixed points. In ordinary thermometers, the two 

 points of reference are the boiling and freezing points of pure 

 water under normal atmospheric pressure, and the interval 

 between them is divided into a definite number of equal spaces 

 depending on the scale adopted, whether centigrade, Fahren- 

 * Preston, Thomas, Theory of Heat (second edition), p. 13. 



Am. Jour. Sci.— Fourth Series, Vol. XXVII, No. 162.— June, 1909. 

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