364 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



still be used, and we have it in our power to go on to 2,000° C, which 

 is quite sufficient for all the more important minerals which we know. 



The physicist has therefore found a suitable melting pot and means 

 of ascertaining what goes on within the pot; but he at once encounters 

 another difficulty. Nature has provided us with relatively few min- 

 erals of high chemical purity. If a natural mineral is chosen for ex- 

 periment, however typical it may be, several per cent of other min- 

 erals may be expected to be present with it, the effect of which is at 

 present quite unknown. Now, the first axiom of the investigator in 

 a new field who desires to undertake measurements which shall have 

 a real value is that the number of unknown quantities in his equa- 

 tions must not be greater than he can eUminate by his experimental 

 processes; in other words, he must begin with 'conditions so simple 

 that the relation between a particular effect and its cause can be 

 absolutely estabhshed without leaving undetermined factors. Hav- 

 ing solved the simple case, it is a straightforward matter to utilize 

 this information to help solve a more compUcated one. Therefore if 

 we would reduce the mineral relations to an exact science, which is 

 our obvious purpose, it is necessary from the outset to prepare mm- 

 erals of the highest purity and to estabhsh their properties. Having 

 obtained such a pure mineral type, it may be, and often is, in the 

 power of the mineralogist and his microscope to determine, by direct 

 comparison with its natural prototype, the kind and amount of effect 

 actually produced in the natural mineral by the one or more other 

 minerals wliich it contains. We have therefore hardly started upon 

 our investigation before the need of an organized system is demon- 

 strated : First comes the chemist, who prepares and analyzes the pure 

 mineral for investigation; then the physicist, who pro^ddes and meas- 

 ures the conditions to which it is subjected; then the mineralogist, 

 who establishes its optical properties in relation to the corresponding 

 natural minerals. 



Having prepared such a mineral, of high purity and of known 

 crystalhne character, we can ascertain its behavior at the tempera- 

 tures which must have obtained during the various stages of earth 

 formation. We can study the various crystal forms through wliich 

 it passes on heating and the temperature ranges within wMch these 

 forms are stable; we can also melt it and measure the melting or 

 solidifying temperature. Another mineral, prepared with the same 

 care and studied in the same way, may afterwards be added to the 

 first, and the relation of these two determined. If they combine, 

 heat is absorbed or released ; and this quantity of heat can be meas- 

 ured, together with the exact temperature at which the absorption 

 or release takes place. If the mixture results in the formation of 

 one or more mineral compounds, we shall learn the conditions of for- 



