071 the Flexih'ility and Strength of Stones. 293 



The Dundee sfone is from the Myhie-ficld quarry, near Dun- 

 dee; the specimen tried is superior to the kind usually raised 

 from that quarry both in fineness of texture and density. Its 

 specific gravity is 2'621, and it absorbs only -j-J-j- of its weight 

 of water. 



The Craigleiih stone is a fine specimen from the quarries of 

 that name near Edinburgh. Specific gravity 2*362, and absorbs 

 ^-j of its weight of water. 



The Hailes quarry stone is also from near Edinburgh, and from 

 the same stratum as the Craigleith, but differs from it in being 

 more laminated. 



Long-annet stone is also about of the same kind as Craig- 

 leith; the 7-inch length was a variety of a coarser texture; 

 the other was a fragment of the piece of which the flexure was 

 measuied. 



The specimens of Bath and Portland stone were good of their 

 respective kinds, and such as are usually employed about Lon- 

 don. 



5. In order to compare the results of these experiments, I will 

 use the following formulae ; in which iv is the weight that pro- 

 duces a deflexion S ; and VV the vveight that broke the piece ; 

 J being the depression at the time of fracture ; ^ = half the 

 length; I = the breadth; and d = the depth. 



■ = The weight of the modulus of elasticity, or measure 

 of the elastic force*. 



■ = The extension at the time of fracture. 



3 ' W 



— — = The cohesive force of the material, on the supposi- 

 tion that the resistance to tension is equal to the resistance to 

 compression. 



As the elastic force of a substance appears to decrease when 

 the strain much exceeds about half the cohesive force, in calcu- 

 lating the elastic force the weight w will be taken, which is 

 nearest to half the weight that broke the piece. 



The hardness was compared by scratching a piece of each stone 

 with the same piece of steel, applied in the same manner, and, 

 as nearly as 1 could judge, with the same force. I had not an 

 apparatus fit for the purpose, or I would have used Perronet's 

 method of determining the hardness. The last column of the 

 table shows the order of hardness, making the softest 1. 



• Dr. Young's Nat. Phil. vol. ii. art. 326. 



Tal'le 



