On the Intimate Structure of Crystals. 



277 



These results, however, are merely approximate,* for, as Professor 

 Miers has pointed out to me, the diameter of the second sphere in a 

 cube cannot be obtained by simply subtracting the diameter of the 

 other from the edge. Professor Miers shows that the relation 

 between the length of the edge of the cube (A) and of the radius 

 of the larger spheres (B) and of the smaller (r) may be expressed 

 by the equation 



(R+r) 2 = [A- 

 from which he obtains 



or 



E = 

 r = 



Employing this formula, the diameters of the atoms are found to 

 be as follows : 



Lithium chloride ........ Li 



Sodium chloride .. ...... Ta 



Potassium chloride ...... K 



Sodium bromide ........ Na 



Potassium bromide ...... K 



Potassium iodide ........ K 



Sodium iodide .......... Na 



There does not appear to be any sound reason why the volume of 

 an element should remain absolutely constant and independent of the 

 element with which it is associated, even in a homologous series, and I 

 am inclined to think that the differences which appear in our investi- 

 gation are not wholly due to defects in our knowledge of the specific 



* It has since occurred to me that a slight modification in our conception of the 

 manner in which the atoms are arranged will render our determinations exact ; 

 this will be the case if we consider the atoms to be situated with their centres on 

 the nodes of a cubic lattice ; we shall recur to this in a subsequent part of this 

 communi catio n . 



