Paekee & Dalladat. 



Fig. 1. 



Interference-fringes formed by reflexion from a 

 Class plate distorted by cement, and having 

 a quartz proof-plane resting upon it. Exa- 

 mined by light from a mercury vacuum arc 

 lamp. 



Fig. 2. 



Two disks of glass in optical con- 

 tact. A diamond-cut through 

 one does not spread to the- 

 other. 



Fig. 3. 



Corner broken from a cell, showing that the fracture travelled without hindrance 

 across the joint (AA) (xb diameters). 



Fig. 4. 



Small glass plate (X6 diameters), showing 

 portion torn from another plate heated in 

 optical contact with it. 



Fig. 5. 



Cell after putting windows on in optical contact, 

 heating, and then subjecting to severe mechanical 

 strain. Windows net perfectly joined. 



