430 



APPENDIX. 



No. 1. 



Europe and Asia. A true arch is formed of a series of wedgCrlike stones 

 or of bricks, supporting each other, and all bound firmly together by the 

 pressure of the centre one upon them, which latter is therefore distinguish- 

 ed by the name of keystone. 



It would seem that the arch, as thus defined, and as used by the Romans, 

 was not known to the Greeks in the early periods of their history, other- 

 wise a language so copious as theirs, and of such ready application, would 

 not have wanted a name properly Greek by which to distinguish it. The 



