1883.] 



on ilie Size of Atoms. 



201 



vibration tlie direction of one of the other two direct lines of the 

 cubic arrangement. 



You have also before you this series of diagrams (Figs. 4 to 9) of 



Fm. 8. 



Fig. 9. 



<r 



Two particles in Wave-Length. 



waves in a molecularly-constituted elastic solid. These two diagrams 

 (Figs. 4 and 5) illustrate a wave in which there are twelve molecules 

 in the wave-length ; this one (Fig. 4) showing (by the length and 



