AS TO SOUNDNESS. 61 
We have, then, two arches crossing each other at right 
angles, which have ¢he same centre of weight. The centre 
or focus of weight is at the coffin-joint,—please remember 
that. After passing this joint the weight vadzates, and so 
gets diffused. In radiating, the rays pass from this 
joint through the coffin bone, which is itself a radiating 
structure, on to the entire base of the foot, the most 
direct, therefore the shortest rays, as I have already 
told you, pass out at the point of the frog. 
Let us stop a moment to consider the difference in 
intensity between focused and diffused rays. In the case 
of light, you can focus with a magnifying glass the rays 
on the back of your hand until you get an intensely 
bright spot about the size of a pea, when all the rest of 
the back of your hand appears in shade; but move the 
glass nearer to or further away from your hand, and you 
see the bright spot becomes larger and larger, darker and 
darker, until it ceases to be discerned as a spot at all, 
and the back of your hand is not now in the shade, but 
is faintly lighted up. The rays have radiated, and now 
cover a wider area, and fazz//y light up this area, instead 
of lughting an area the size of a pea zzfensely and leaving 
all the rest dark. This you can see. In your penny- 
peep-show days you will no doubt have seen a large 
muscular mountebank lie upon his back, and have a 
large size forge anvil placed upon his chest, and this 
struck by the swinging blow of a very large sledge- 
hammer. The centre, or focus ef weight, here is the 
face of the hammer upon the anvil, and the rays have the 
