Stoney — On Texture in Media, etc. 399 



Hocks Ax Ay As is sufficiently large to include an enormous 

 number of the individual operations that are in reality what 

 actually go on in the medium. 



We come upon the same result when we make a similar inquiry 

 with regard to solids. But I forbear going into numerical details 

 in this branch of our subject until I can publish investigations on 

 which I was engaged some years ago, by which it appears that 

 the form and dynamical properties of many crystals can be con- 

 nected with their chemical constitution. When this subject is 

 gone into it becomes plain that the dynamical properties of solids 

 also, such as their power of propagating shearing stresses, are, like 

 those of liquids and gases, due to events of an utterly different 

 kind that occur between parts so close, and in periods of time so 

 brief, that enormous shoals of these events occur in a very small 

 fraction of a second, within elements of volume many times 

 smaller than the most tiny spec the microscope can show. Ac- 

 cordingly, what we regard as dynamical properties of solids, such 

 as their power of propagating tensile, compressive, shearing, and 

 twisting stresses, are an outcome of what I have called the texture 

 of the medium ; and only appear between blocks so large that in 

 considering the effect of one of these large blocks upon its neigh- 

 bours, we need only take account of the general outcome that 

 emerges when vast numbers of the individual events that are 

 actually going on are combined, and their general drift obtained 

 by a statistical method. 



It is especially instructive in this connexion to consider the 

 problems of that branch of dynamics which is called Rigid Dyna- 

 mics — such as the investigation of the motions of a top, or hoop, 

 or of the precessional motion of the Earth. In these inquiries the 

 integral calculus is employed. But the integrations are all such 

 that the calculated motions of such bodies would come out almost 

 precisely the same, whether the absolute limit, as furnished by the 

 integrals, be taken, or a summation for which the volume of the 

 rigid body is regarded as divided into blocks as large as the 

 smallest specs visible in the microscope. It is desirable, however, 

 that we should bear in mind that there is the widest difference 

 between the physical assumjjfions underlying these tivo methods of 

 procedure. 



If we proceed by integration it is tacitly assumed that the 



