158 CARNEGIE INSTITUTION OF WASHINGTON. 



of anything in such a field as this, for it is plain that mere observation of 

 a process of change without being able to determine the points between 

 which the change was occurring would rarely permit of reproduction, 

 still less of definition. Without the power of reproduction, or of 

 definition in terms of the state of the participating materials, or the 

 magnitude of the participating forces, anything approaching a science 

 of rock formation or of mineral chemistry is little more than a concept — 

 a desideratum without tangible reality. 



To-day the telescopic picture is quite different. The field has been 

 brought nearer and many details of it are now in plain view. Tem- 

 peratures appropriate to the rock-forming processes can be provided 

 without difficulty and measured with but little more uncertainty than 

 the temperatures of every-day life. Pressures adequate to insure the 

 participation of the more volatile ingredients of rock formation are also 

 available and properly subject to control and measurement. Criteria 

 have not been found lacking through which to recognize and define 

 equilibrium, together with the magnitude and direction of its dis- 

 placement with changes in the reacting forces. Heat changes are 

 determinable both in quantity and direction. Latterly, even the 

 atomic composition and structure of the participating crystalline 

 minerals are becoming capable of photographic record. In short, there 

 is abundant experience now available through which we may assure 

 ourselves that the relations between minerals participating in rock 

 formation are orderly and subject to precisely the same laws as 

 similar relations in solutions in more conventional physical chemistry. 



In consequence of these assurances, obtained after the expenditure 

 of much effort and ingenuity, the character of the program of geo- 

 physical research from year to year may be seen to change very 

 appreciably both in this Laboratory and elsewhere. It is not so much 

 a matter for discussion now as formerly, whether this or that method 

 of temperature measurement is competent in a temperature region 

 which is difficult of access, or whether the moment of change of state 

 is revealed by the appearance of a melting mineral or solution. The 

 competence of observations of this kind is now capable of precise 

 appraisal and many modes of verification are available. In con- 

 sequence of such progress the agenda-list in any recent year will be 

 found to contain progressively more of the application of recognized 

 methods to current geologic problems, while less attention is given to 

 the elaboration of the methods themselves. In terms of the whole 

 effort expended, the major portion of the task hitherto has been con- 

 cerned with the demonstration of the effectiveness of certain lines of 

 study and of the scope and trustworthiness of the available methods 

 of attack. So far as these efforts have been successful, hitherto inac- 

 cessible problems in the earth's formation now lie open for study and 

 are being attacked with increasing success. 



