66o THE POPULAR SCIENCE MONTHLY. 



weathering are to be seen in Greyfriars Churchyard. On the south 

 wall, in the inelosure of a well-known county family, there is an 

 oblong upright marble slab measuring 30:^ inches in height by 22f 

 inches in breadth, and three fourths of an inch in thickness, facing 

 west. The last inscription on it bears the date 1838, at which time 

 it was no doubt still smooth and upright. Since then, however, it has 

 escaped from its fastenings on either side, though still held firmly at 

 the top and bottom. It consequently projects from the wall like a 

 well-filled sail. The axis of curvature is of course parallel to the u])- 

 per and lower margins, and the amount of curvature from the original 

 vertical line is fully two and a half inches, so that the hand and ann can 

 be inserted between the curved marble and the perfectly vertical and 

 undisturbed wall to which it was fixed. At the lower end of this slab 

 a minor curvature, to the extent of one eighth of an inch, is obsei*v- 

 able coincident with the longer axes of the stone. In both cases the 

 direction of the bending has been determined by the position of the 

 inclosing solid frame of sandstone which resisted the internal expan- 

 sion of the marble. Freed from its fastenings at either side, the stone 

 has assumed a simple wave-like curve. But the tension has become 

 so great that a series of rents has appeared along the crest of the fold. 

 One of these has a breadth of one tenth of an inch at its oj^ening.* 

 Not only has the slab been ruptured, but its crust has likewise yielded 

 to the strain, and has broken up into a network of cracks, and some of 

 the isolated portions are beginning to curl up at the edges, exposing 

 the crumbling, decayed marble below. I should add that such has 

 been the expansive force of the marble that the part of the sandstone 

 block in the upper part of the frame exposed to the direct pressure 

 has begun to exfoliate, though elsewhere the stone is quite sound. 



More advanced stages of curvature and fracture may be noticed 

 on many other tombstones in the same burying-place. One of the 

 most conspicuous of these has a peculiar interest from the fact that it 

 occurs on the tablet erected to the memory of one of the most illustri- 

 ous dead whose dust lies within the precincts of the Greyfriars the 

 great Joseph Black. He died in 1799. In the center of the sumptu- 

 ous tomb raised over his grave is inserted a large upright slab of white 

 marble, which, facing south, is protected from the weather partly by 

 heavy overhanging masonry, and partly by a high stone wall immedi- 

 ately to the west. On this slab a Latin inscription records with pious 

 reverence the genius and achievements of the discoverer of carbonic 

 acid and latent heat, and adds that his friends wished to mark his rest- 

 ing-place by the marble while it should last. Less than eighty years, 

 however, have suflSced to render the inscrijition already partly illegi- 

 ble. The stone, still firmly held all round its margin, has bulged out 



* It is a further curious fact that the slab measures half an inch more in breadth 

 across the center, where it has had room to expand, than at the top, where it has been 

 tightly jammed between the sandstone slabs. 



