536 



Royal Society : — 



our acquaintance with its strength in the various forms In which it 

 is employed in the arts and in scientific research is very hmited. 

 To arrive at satisfactory conchisions, the experiments on this mate- 

 rial were extended so as to embrace the direct tenacity, the resist- 

 ance to compression, and the resistance to bursting, as well as the 

 resistance to collapse. 



The glass experimented upon was of three kinds ; — 



Specific gravity. 



Best flint-glass 3-0782 



Common green glass 2"5284 



Extra white crown-glass. . . . 2*4504 



Tenacity of Glass. — For reasons detailed by the authors, the ex- 

 periments upon the direct tenacity of glass made by tearing speci- 

 mens asunder are less satisfactory than those in the rest of the 

 paper ; and it is argued that more reliance is to be placed upon the 

 tenacity deduced from the experiments on the resistance of globes 

 to bursting in which water-pressure was employed, than upon the 

 tenacity obtained directly by tearing specimens asunder. The 

 results obtained by the latter method give the following mean 

 results : — Tenacity per square inch 



in pounds. 



Flint-glass 2413 



Green glass 2896 



Cro'wn-glass 2346 



Resistance of Glass to Crushing. — The experiments in this section 

 were made upon small cylinders and cubes of glass crushed between 

 parallel steel surfaces by means of a lever. The cylinders were cut 

 of the required length from rods drawn to the required diameter, 

 when molten, and then annealed, in this way retaining the exterior 

 and first cooled skin of glass. The cubes were cut from much 

 larger portions, and were in consequence probably in a less perfect 

 condition as regards annealing. Hence, as might have been antici- 

 pated, the results upon the two classes of specimens, although cou- 

 sistent in each case, differ widely from one another. 



The mean compressive resistance of the cylinders, varying in 

 height from 1 to 2 inches, and about 0*75 inch in diameter, is given 

 in the following Table : — 



