GEOPHYSICAL LABORATORY. 161 



The usefulness of these observations is obviously great, because 

 a knowledge of the exact location of the atoms in a body makes possible 

 not only some sort of an intelligent discussion of the manner in which 

 they are bound together, but also should serve as a basis upon which 

 to build quantitative measurements of the forces operating within 

 solid bodies. "WTien combined with other information which seems to 

 bear upon the nature of the forces of chemical combination, a knowl- 

 edge of the crystal structure of a compound may not only indicate the 

 probable way in which the atoms are related chemically to one another, 

 but may even tell something of the internal structure of the atom 

 itself. To illustrate, it was shown, in the course of studying the mem- 

 bers of the calcite group of minerals, that the oxygen and carbon atoms 

 in these carbonates are always associated together in exactly the same 

 way, even though the relations of these atoms to the others present 

 differ from one compound to another, thus pointing quite clearly to 

 the existence of definite groups of atoms in the solid crystal. At the 

 same time it became evident that on the basis of our present knowledge 

 it is quite impossible for the outside electrons of these atoms to be 

 arranged at the corners of cubes, as some have assumed to be the case 

 with all atoms. 



Again, an attempt to explain quantitatively the diffraction of X-rays 

 leads immediately to the formulation of definite hypotheses as to the 

 entire internal structure of the atom and gives a criterion whereby their 

 probable correctness may be gaged. 



These earlier methods of study are applicable only to the simplest 

 of bodies. It consequently has been necessary to attempt to develop 

 a way of investigating the structure of crystals which would be capable 

 of application to the more complicated, but more interesting and im- 

 portant, substances. A brief outline of such a method and its applica- 

 tion to two rather simple crystals has been given in recent publications 

 from this Laborator3^ A more detailed discussion of this subject will, 

 it is hoped, appear shortly as a book. 



Diffraction effects of this sort can be obtained not only from indi- 

 vidual crystals, but as well from any material in which the atoms 

 stand in a regular relation to one another. We, therefore, have 

 offered to us the possibility, and it is yet for the most part only a 

 possibility, of studying the intimate structure not only of crystalline 

 powders and little understood "liquid crystals," but even of some 

 liquids. Many interesting questions thus present themselves; for 

 instance, do the atoms within the molecules of complicated organic 

 substances bear definite spacial relationships to one another even in 

 the liquid state? are the individual particles of a colloidal suspension 

 made up of a definite and orderly or of a haphazard grouping of atoms? 

 what happens to the intimate structure of a compound when it takes 

 another substance into solid solution with itself? is a particular rock 

 substance, the hydrated silicate of copper, chrysocolla, for example, or 



